#40 is very short (when used to shave on a pair of clippers) it is usually what they use when prepping for surgery (unless they go shorter). A #10 blade is used most often by groomers to shave bellies, faces (poodles ect)...it leaves hair about 1/8 of an inch.
I do not think the #10 blade brushed along a rotties back would catch as much of the loose hairs. The blades are farther apart. Farther apart blades when used to strip (like a furminator) will leave a smoother appearance as they do not take as much hair off.
Anyways, don't worry about poking him...the cheap one will be fine. I usually pull the skin on the back away from the spine to brush (Nisha is kinda skinny)...this way it is not raking against her bones. Brush in short firm strokes; let us know what you think of it
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Sorry if all this confuses you!!