I've had the same metronome app for almost 5 years because it just works, and I paid 99 cents for it a few years back. That changed this last weekend. I discovered Pro Metronome, and promptly paid the $2.99 for the pro version of it.
Why? Because it has one amazing feature: it allows you to slowly speed up your tempo over a set number of measures. I've been using it to practice my 12-bar blues, starting at 90 BPM and ending at 150 BPM, increasing by 5 BPM every 12 measures. It's been a tiny but noticeable performance boost in my home practicing, and well worth the few dollars.
You can download it for free here, but the full version is $2.99 . Happy practicing!
One note: I am not endorsed, affiliated, or getting paid to use this product in any way. I just love it.