WD: I haven't done a side-by-side comparison, but I did inspect thoroughly the Senior Reamer at my Tinder Box. They are comparable in a number of ways, but I find the Kleen Reem to be of a bit better craftsmanship (not by much) and the drill bit in the handle is longer and stouter on the Kleen Reem.
My only complaint with the Kleen Reem is the drill bit itself: it's made of a particularly soft metal, and I've found it bent once or twice, needing to be re-straightened. What I think happens is as it is used, the offset of material inherent to the engineering of any drill bit, it can't stand side-to-side motion very well, and when using something that requires a static pivot point is used by hand, it will warp. The hand isn't accurate like machinery, and even using it at a slight angle could prove problematic. A warp in a drill bit in a shank could start hitting briar in the shank and airway before you know it.
Otherwise, I paid a staggering sum of $10 for my Kleen Reem, and it wasn't a museum piece, and does the job when I need it (which is rare--I prefer constant maintenance with a cheap pipe nail).
Harbor Freight, every man's cheap toy store, has these hand-held aluminum "hand chucks" for securing a drill bit that I'm thinking of getting so I can use my own real drill bits of correct sizes for the airways of my pipes.
8)