I'm a bass player and decided for the Hypergravity Mini over the SpectraComp because it has more knobs. It just seemed to be too much of a hassle, trying to control a Compressor using only one knob. Apart from that, they are, as far as I know, identical, internally.
The Hypergravity Mini is a 3-band compressor in a tiny, well-build pedal. Which in itself is already amazing. Since it is a digital pedal, it doesn't color your tone other than what you tell it to. The Toneprint editor makes it configurable beyond what anyone could want from a 3-band compressor in pedal format.
There are two apps, the Toneprint app for iOS and Android, which let's you beam available artist Toneprints (pedal configurations) to your pedal by holding your phone to your guitar pickup. Then there is the Toneprint editor for Windows, OSX and iOS (tablets only, I think), which is where things get really interesting. It let's you configure any parameter you can think of in a compressor (threshold, ratio, attack, hold, release, x-over frequencies, did I forget any? probably...) for each of the bands or all of them at once, assign each knob to up to three of these parameters and define the ranges the knobs should cover for each of them. You can also turn off bands, and use it as a one or two band compressor. The editor lets you store different configurations on your computer and put one onto the pedal via USB.
If you can't be bothered fiddling with all this detail, just try the available artist Toneprints and go with the one you like. If you are a bass player, consider going for the SpectraComp in this case, since there is only one artist Toneprint for bass in the Hypergravity, as of this writing and even though the pedals are apparently identical, internally, the Toneprints are not compatible.
The one minor complaint I have with Toneprint in general, is that there is no editor for Android. If you want to use more than one custom Toneprint on the road, you need an iPad or bring your laptop. This is acceptable for a compressor, where you would likely only use one configuration anyway, but I could imagine, that this could become a bit tedious with other pedals, where you potentially use more than one custom Toneprint. But then, other pedals only have one "configuration" in the first place, so what am I complaining about? ;)
In conclusion, I'm very happy with this purchase. Especially considering the price.