The problem with straight keyboards is that they are straight, while your arms are not straight. You therefore have to turn your wrists outwards so that your hands are roughly parallel. This creates tensions that may eventually result in expensive physiotherapy courses and/or job-terminating pain. Some people get carpal tunnel syndrome, tennis elbow, writer's cramp, housemaid's knee, Nintendo thumb, iPad neck and other repetitive strain injuries, and some people don't. Life isn't fair.
The obvious solution is to move the keys so don't have to swivel your wrists, which means the keys on the left hand side will be at different angle from the keys on the right hand side. Microsoft Comfort and Sculpt keyboards do this, and they work well for a lot of people. I've used them myself.
My problem was that I wanted a bigger split, and preferably an adjustable split, so my next step was an adjustable Fujitsu KBPC keyboard, which I bought for £29.99 in May 2014. The action was somewhat soft and squishy, and a couple of keys eventually started to stick, so it hit the junk pile towards the end of last year. However, I'd used it quite happily for 31 months, so it wasn't bad value.
Either way, I had learned that I was happier with a bigger split than Microsoft provided. When I started using the Fujitsu, the split was quite small, but it gradually got wider. The next logical step was a keyboard that allowed for a complete split, so last December, I bought a Kinesis Freestyle 2 (UK layout) for Windows on Amazon.co.uk, for the princely sum of £82.99. (It works on Linux, too, but not all the special keys are supported.)
In this case, my main worry was key quality. In the 1980s, I fell in love with the buckling-spring IBM Model M, and I used variants for decades. They don't wear out. I would really like a split ergonomic keyboard with similar mechanical keys at an affordable price. There don't seem to be any. The Freestyle 2 is a good quality membrane keyboard, but there are cheaper non-ergonomic keyboards with mechanical keys.
My Freestyle 2 arrived in a plain white cardboard box along with a single piece of paper: the instructions. I needed them. After I plugged the keyboard into a USB port, the right side keys didn't type the correct alphabetical characters. The blurb explained that the Fn key, which I had pressed by accident, toggled numbers and odd characters on that side of the keyboard, not just on the row of Function keys. Sadly, apart from the labelled numeric keypad (789 UIO JKL), I don't remember any of them, except that Fn-F11 runs the Windows Calculator.
Another oddity is the Insert key, which I rarely use. The Fn key puts Insert onto the Pause Break key, which I never use at all.
Worst of all, I have struggled with the four special keys down the right edge, which are, from top to bottom: Home, End, Page Up and Page Down. Unless I look first, I often hit the wrong one. I would prefer the keys to be side by side, as they are on the Fujitsu and other less compact keyboards. If not, I'd rather they went: Home, Page Up, Page Down, End.
When you hit the wrong key, the results can be disconcerting, and I've never had problems like these before.
The left-side part of the keyboard includes a gratifyingly large Esc key, plus 10 keys I may never use. Five are for Cut, Copy, Paste, Del and Undo, but I've spent decades using Ctrl combinations that work on every PC keyboard. Two keys are for forward and back in a web browser, where I already use Alt and an arrow key. I'd rather have the Home, End, Page Up and Page Down keys there, side by side, though that would be very non-standard indeed.
I'm still tempted to try it, but this is a "driverless keyboard" and the keys are not programmable. However, I assume I could change them with a keyboard remapper.
I dithered before buying the Freestyle 2 for only one reason: it doesn't have mechanical keys. However, the touch is actually nicer than I expected. It feels like an upgraded version of one of the better Dell keyboards such as the SK-8115, though I no longer have one around that's suitable for comparison.
The keys are not clicky but they are quite tactile, have plenty of travel, and - for a traditional keyboard - a relatively light touch. Kinesis says their key switch has "a typical average key force of 45 grams, approximately 25 percent less than most other keyboards". (I learned to touch-type on typewriters and still have a heavy action.)
After a couple of months with the Freestyle 2, I no longer notice the action when I'm working, which is as it should be. However, my typing speed is about 10 percent down on what it was with the mushier Fujitsu KBPC keyboard. There may be several reasons for this. One is that my hands are now so far apart that it's harder to cheat on touch-typing. I probably need to do some practice drills to correct my bad habits.
Mechanical keyboards are popular with gamers, and there are plenty of cheap models available. It's therefore surprising that you still can't get a good, reasonably priced ergonomic version. There may be a gap in the market that the Freestyle 2 doesn't fill.
The Freestyle 2's competitors include the Matias UK Ergo Pro Quiet, which I have not tried for two reasons. First, it scores badly in reviews at Amazon.co.uk: in fact, the only 5-star review is by someone who "only received this keyboard today". Second, the current UK price is £186. For that sort of money, I'd want my choice of Cherry MX switches, not Matias keys that one Amazon reviewer describes as "spongey and a little nasty" (sic).
Perhaps the market isn't big enough. After all, most people will probably settle for a Microsoft Sculpt, which is only £66.39 including a number pad and mouse, or a Microsoft Ergo keyboard at roughly half the price. (The number pad for the Freestyle 2 costs over £90.)
In that context, the idea of buying a totally-split keyboard, like the Freestyle 2, is a little scary.
If you take the leap, remember it's not an instant fix. You need to be a reasonable touch-typist to use it properly, and even then, you will have to get used to it. I'm still doing that.
Either way, I think it's a good idea to go ergonomic before you need physiotherapy, not, like me, afterwards.
Update: Kinesis says it will be launching a Kickstarter for the Kinesis Edge gamer's keyboard. This is basically a Freestyle 2 with Cherry mechanical switches. There are some details on the Kinesis website.