K&K Pure Preamp

I have an acoustic guitar with pasive K&K pure pickup which really benefit from the gain boost.

The preamp gives a slight mid boost, which seems a reasonable default (this can be turned up or down, after taking off the cover, with a small screwdriver). You get a decent EQ (bass. mid, treble) on top of that, so you will probably never need to change the default settings but it's a nice touch that it is available.
It's light, small, probably will just sit on your belt (clip on is attached) so you can reach it while you're playing.

I have also tested this with my electric guitar and was surprised how well it sounds. It's almost transparent, just gives you more headroom and a decent signal boost.

Be aware that since it's supposed to be on your hip the only option is battery power (standard 9V).

The cover sits tight and I have to wrestle a bit with it every time. I suppose it's better than it would be falling off on its own, but the design could be improved here somewhat.

Build quality is great, seems like a thing you won't be afraid to chuck in your backpack without worrying it.

The EQ pots are a tad small, but this is not a deal breaker.