I too have a Maximum Motorsports bar (4-point). I love it. The mounting points are very well selected, mounting brackets are well designed, and the fabrication is top notch. You'll still need a welder to finish off the two rear struts (they initially bolt in to establish precise fitment, then you take the whole bar out and weld them permanently to the main hoop). So be aware it isn't a completely bolt-in process.
As for structural integrity, it's smartly built. The main hoops come down into the TOP of the rear bulkhead (that's one of the primary structural components of the chassis) not the floor pan - it never touches the floor pan. The brackets they have for this replace the OEM gusset bracket at those points and they're much stronger than the factory ones. The rear struts are sent to the wheel arch with large area pads that are formed to fit around the arch and sandwich the OEM steel with equally sized back plates in the wheel well. I got the road race unit with triangulated cross brace, since I didn't care about trying to preserve the functionality of the back seat. I have the highest confidence in their design.
I have no doubt that a well built (i.e. designed and fabricated) fully welded in 4-point bar would have some marginal advantage over a bolt-in unit (all things being equal), but I'd be very surprised if it was much (and perhaps would be of greater benefit if it was designed to tie in and reinforce the rear shock mount area, like the Rehagen/FR500S bars do...which, even so, IMO are only important for coil over set ups). I could always weld in the bar I have if I wanted to, and I'd be happy to match it up against any other custom 4-point bar out there. The MM bar is really very well done.
Best,
-j