Those who use older iPhones tend to look at new iOS releases with a hint of suspicion. After all, installing a new iOS update can cause performance problems, and since updating is essentially a one-way journey, it can be problematic to install it on a gamble.
So, will iOS 12.4 slow down your iPhone?
In testing I've carried out, my answer is a conclusive "no." Older iOS devices operate and run as they did under iOS 12.3.1.
However, the downside to this is that there's no performance boost from installing the new update either, which means if your device felt old and sluggish under iOS 12.3.1, then iOS 12.4 isn't going to make it any better. This is particularly true for the iPhone 5S and iPhone 6.
iAppleBytes carried out side-by-side testing of iOS 12.3.1 and iOS 12.4 across a range of devices, and this came to the same conclusion – iOS 12.4 isn't a performance hog.
It also seems like iOS 12.4 is also kind to battery life, so there doesn't seem to be any shocks for people after installing it.
So if you've not done so already, get it now.