I don't like the idea of the full length slot on those. You're never going to need all that adjustment. To me it looks like it'll be able to twist and flex more due to the slot. I didn't try one,because despite being made in China I could only find one to buy from the USA, which makes shipping more expensive than the item, for me.
You can use some aluminum plate to make your own mount, and the pulley wheel from a mountain bike chain retainer or single-speed converter. The pulleys generally have decent bearings and durable plastic, at least. I attached mine using four stainless steel P clips (no rubber though), and it seems pretty stiff. Instead of the slot for adjustable pulley position I just measured up where pulley needed to be to lift the chain over the chainstay and drilled a single hole.