The Opus falls in the the cheap catagory, for reliable, what is your intended usage, if hitting the trails a couple of time a week, and actually riding off road, a bike like that will last a few months before thing start breaking / wearing out, and it's generally tired, if riding MUP's or fire roads, the toll on the bike won't be as hard, and it should last a lot longer.

From the spec listed, the forks are non serviceable Suntours, when they wear out, whcih they will, they will need replacement, as parts are generally not avaliable, and the cost of a service would be more than the replacement cost. The rear wheel is a freewheel hub, going by the TZ21 freewheel fitted, freewheels are bad for going off road, as the axle isn't supported as a freehub's is, so if going off road, budget for replacement axles / wheels.

For the brand, never heard of them mentioned on BF before, the advantage of say a Specalized or Trek, is better warranty, although maybe not quite as good value, you have to work out what you want for value for money to what you