Don,
I have used all three on selfbows. The UBR is a well thought out product, I really like the double handle. It is a tad more aggressive than the 49 on the coarse side but not so much so that the removal of rasping marks is impossible. I do wish however that it had a half round side as do the Nicholson 49 & 50.
If I could have only one I would buy the 50. While , It is a little slower in stock removal and needs a little more cleaning it very easy to remove the tooling marks it leaves behind. I find it in my hand more than the other two rasps.
Hope this helps.
Sean