yeah first thing I'd do is make a tensionable belt. Sounds like they loosen a couple bolts, pull the roller to tension and lock with bolts. I'd make it so the bolts tensioned the bed.
It might work like that. Info is not great. No idea what the belt is made of either.
I'd also add vertical supports between the ends of the angled rods and the base. Just remove any extra vibration from the extruder.

But given the price point of the other belt machines I've seen - this is a serious bit of kit, at a very affordable price.
I have nowhere to put one or the money for one, but I'd quite like one all the same, lol