Su-16 is super lightweight...shoots fine nothing special either way.
But between the 3 its at the low end of the spectrum. It works and is the cheapest of the bunch, but you will feel like your holding a glorified nerf gun. It IS all plastic and it IS held together by way too many screws. Its reliable enough and shoots about average for what you'd expect out of an econo rifle. It just FEELS like your holding a plastic gun, because thats what it is. Did I meantion its the cheapest of the 3? The folding stock bipod fixture is garbage and an annoying affair to reposition. Purchasing the ar stock added about a dozen more screws to the side, making you wonder if you should run out for that extra 3 tubes of loctite or post in an XCR forum about where to buy bulk 242 for your XCR...err...you mean SU16 but we won't tell. At this point your also into the 4 digit range costwise for again...lots of plastic. Or polymer if that word makes you feel better.
This would make a great truck gun if you let it fold...or a survival gun? Occasional plinker? I'm not sure, just looking at the finish dissapear from the barrel after folding the stock folding forend a few times turned me off fast.
Did I mention this is the most affordable of the 3? Thats about the greatest saving grace.
The MR1 hits the high end of the scale between the 3. It is by far the HEAVIEST of the 3, to the point where you hold it and wonder why the heck any 556 should weigh this much, or if your holding the new Barret in .80 caliber Humongosaurus rex. It has ergonomics that are eccentric, with a mag release only its maker could love requiring 2 hands to properly operate. It does wear the Benelli badge with pride, offering high quality parts and finish throughout, and a piston system that looks like it was designed to enable reliable feeding of 120mm APHEFSDS rounds not .223, hence the added weight. That being said, you KNOW this thing is going to be reliable due to that overbuilt piston. Visually you either love her or hate her, but it can grow on you. Aftermarket is practically non-existant, owing itself thusfar to the 1 propietary tri-rail system that costs 5x as much as it should for a piece of plastic no bigger than a credit card. The barrel, while thin has Benelli's signature dipping process allowing it to remain ultra-thin while providing very good accuracy and heat resistance in rapid fire. Scoping can give you a cheek rest that would suit dolph lundgrens massive square jaw unless you remove the rear sight. Personally I only ever had teh fixed stock, finding the adjustable on the MR1 to look like some sort of space age manta ray fixture.
Overall its ECCENTRIC. Something I would highly recommend you TRY BEFORE YOU BUY. It is NOT your current wunderwaffen that is 90% of all rifles currently built similar if not exactly like a modern AR. That can be a GOOD thing depending on your needs, but it is also a DIFFERENT rifle.
Now the CSA 556 rifles. I'm biased but only because I've owned all 3 and this is the only 1 out of the 3 I've kept.
It is a sub 1000$ rifle that is built all metal parts with a high quality finish. It is simple to strip and clean, quicker than either the su16 OR mr1. In your hands it FEELS like a rifle designed for the average man to fight off hordes of either rabid squirrels or killer penguins. Aftermarket support is wonderful and the plethora of grips, stocks, forends etc will keep you busy for a long time and satisfy most adult gunlego afficionados, albeit if you want to mount a traditional style scope you may have a little more headache but this is overcomeable. Accuracy is on par with what a millitary-esque rifle should be. With the ar magwell adapter that takes 3 minutes to install it is everything I think a rifle should be. There are also multiple barrel lengths available to suit any tastes from PDW to non-restricted and the CSA rep is even on this board available to answer any and all questions at the mention of a post. THere's a reason the soviets let the Czechs keep this design...Oh and did I mention this is still under 1k CDN even with the magwell adapter?