I'm just now getting my car mounted. Last night I dropped the rear axle from the car and connected the two ends of the rotisserie together. But my car still has a gas tank, doors, front fenders, dash, heater and windshield. The whole process is a bit intimidating. It's a lot of weight, and if it were to fall or spin out of control, it could do some damage or really hurt somebody (me). I'm sure it will be better when I get the rest of the weight off.
You should be able to see in my photo, above, that there are two separate verticle adjustments. One of them raises and lowers the car relative to the pivot point. This allows you to balance the car so it rotates easily and doesn't have a tendancy to spin out of control. I think the two hanging braces in your photo are required as a way to compensate for this lack of adjustment. I'm guessing they hold the car in position, but how do you control the weight while you are rotating the car?
Right now my car is hanging with the center of gravity well below the pivot point and so the car is hanging level and is very stable. But, if I try to rotate the car, it takes tremendous effort. Tonight, I will be playing with the adjustment to raise the center of gravity and make the car easier to rotate. This will be a trial and error process, because I have no idea where the CG is located. Also, this will change as I bolt parts back onto the car after paint is finished. I think not having this adjustablity would be a big problem.
I'm still having trouble seeing how this rotisserie connects to the vehicle. Maybe there are more pieces that are not shown. With mine, the brackets that bolt to the rear bumper mounts are puting a lot of torque on the rotisserie.
I found that the two ends of the rotisserie have a tendancy to lean in towards the car, putting most of the weight on the center wheels. I used a long chain and a come along to pull the two ends together until I intalled the connecting tube down the center. This transferred some of the weight to the outer wheels and made the whole thing roll a lot better. Given this tendancy, I would be cautious about removing that angle support.
The hydraulic rams are nice, but I'm not sure they're really necessary. I think they are for moving between adjusting holes. Once you get it where you want it, you put a bolt into the hole to hold the weight. I wouldn't want to trust the rams to hold the car all the time. If you decide to add them, I know Harbor Freight sells them cheap. Alternatively, you could just put jacks under the car and lift it that way.
As for the strength, it's hard to judge. Like I said in my earlier post, I think mine is overkill. This one may be fine. I do think you should add the angle brackets even if you don't put on the hydraulic rams. Also pay attention to how it locks at a particular angle of rotation. Mine uses two bolts at each end, but they just press on the inner pipe and could easily slip. The larger diameter of the pivot pipes helps somewhat but it's still very important to get everything balanced so these bolts don't slip.
I hope this helps. It could be that I'm being paranoid. I tend not to be risk averse about these things, but this makes me nervous. Before I started hanging the car, I figured no big deal. But when you start actually doing it with your own car, it gets your attention.