Picked one up about six months ago and have to say it's a great little practice amp. Battery life is generally as advertised , roughly 5-6 hours depending on your volume level. The app controlled simulated pedal effects provide for limitless tone choices. Solid product , worth it's cost.
I've heard others say good things about them. I've moved away from modeling amps for the most part, but maybe I'll have to check that one out.
I have the original Spark and I found that it was too bassy until Spark came out with an EQ pedal. That fixed that issue. The other issue I found is that many of the effects chains that I've downloaded seem to be too much. I've found that less is more with these build in pedals.