My experience with a cheap mountain bike was that they're made for the road if anything. The two times i had it off-road, on easy trails (no jumping, nothing as big as riding off a curb, even), I bent a rear wheel each time. Brakes got iffy after a while, adjustments to shifting were ongoing hassle, but otherwise rideable. I did put a new seat on mine, and like you say, it came with the most uncomfortable seat ever- a scheme to sell you that other seat. Anyway, just ride it on the road till it drops dead, or leave it out and don't lock it up or something.
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"be careful this rando stuff is addictive and dan's the 'pusher'."