Is this bike worth the buy? I have someone who is selling it for $400. I don't know too much but I have compared it to a few bikes on 99 Spokes but wouldn't 120mm Travel be too little for a 27.5?
$400 is a good price if the bike is in fair shape. The 710 is the entry level model, so cheapest components, but still a good XC bike. I have a 2014 Altitude 770 Rally Edition, and it is awesome, but much more travel (160/150). The Thunderbolt and Altitude have very similar frames (but 710 is alloy), and the Ride-9 system lets you make minor adjustments to the bike’s geometry by setting the rear shock in 9 different points. If the bike is in good shape, you should buy it. If it is a M or L frame, I’ll buy it if you don’t for $400.
My old RM Element has 80-90mm travel with 26, and it is a very fast XC bike, but there are places I ride the Altitude that I won’t take the Element. The Thunderbolt wasn’t designed as a DH or park bike, but XC and some aggressive trails would be fine. Many guys still ride hardtails; I would much rather 120mm of rear travel than ZERO!