IMO, bushmasters are good rifles... but don't confuse good with mil-spec. They use materials, quality processes, and dimensions that aren't entirely in line with the mil-spec. Some of their barrels are MP (metal particle) inspected for defects (I have one that is, the barrel will be marked "MP), and some aren't. The Front Sight base used with their flat-top uppers requires the use of a 0.40" taller front sight if you want to use any popular BUIS, and every mil-spec detachable carry handle. The bolt carrier keys aren't often properly staked. The list goes on...
With all that said - what all this means to you is completely subjective. Will you be going to the range with it or defending your home? Going to a heavy-use carbine class, or going out to the woods to shoot a few rounds? $700 is a damn good price, and I wouldn't dare sway you away from it... But I would suggest you take a look at what capacity you want this rifle to work in, and compare it to what you can reasonably expect out of it given the level of testing & QA Bushmaster uses.
Also, keep in mind that the rifles that Bushmaster supplies to govt. entities are not guaranteed to be manufactured the same way as the ones you can find in your gun store.
In the interest of full disclosure, I do own a Bushmaster upper, and it's been nothing but aces for me. The FSB thing was annoying, but easily solvable. I've never had a malfunction, but at the same time, I don't shoot it hard either.