Most UBS specifically state NOT to mount them on anything but aluminum rails and handguards. The recoil is likely to damage a plastic rail over time if not immediately. I would take caution mounting it on a tavor even if there's room to do so. Unless you've found a way to reinforce it somehow.
Given the pricing of Turkish shotguns, the extra stock bits likely account for very little of the overall cost. I'm not sure they listen to what the market demands either lol. I'm amazed they took a swing at the UBS at all given it's such a niche market. I would have been happy to just get a short barrel for the existing 870 adapters but this is all a bonus really!