I am not familiar with that particular saw. I would suggest you try it out. Cut and join a couple of frames on it. If it works & the price is right, go for it.
It's still just a machine, you will be able to purchase bearings and parts most any were. If you can't, any machine shop can make replacement parts, as long as you have the old part for them to duplicate. Remember though, it's the blades that really count. A dull or damaged, or cheap blade can make a huge difference in the quality of your frame. The saw can be perfectly good, but if your running cheap blades, you will not get a decent frame.
Try pulling the blades toward you in the direction of the arbor, you should be able to feel it move slightly and return back on it's own. If it does not move, you probably need to replace the bearings. If it moves as I described, and you get a bad cut, it is probably the blades. If the price is right on the saw, anything wrong with it can be corrected by a machinist.
Good blades for a double cut off saw can run from $200.00 each, on up. They last a long time and it is money well spent.
A used double miter saw should cost under $2,00.00
If they want more, I would pass on it. You would be better off to use what they want as a down payment on a brand new CTD or some such thing. With CTD, you will get the best customer support and people who understand our requirements. I am sure this is true with most new saws though.
John