I love the SP101. Here is my experience with testing aftermarket grips with concealment in mind.
Pachmayr Diamond Pro
Super comfortable to shoot, way too soft IMO, does not conceal well due to tacky nature. Great for the range.
Badger Boot
Very uncomfortable to shoot, small, awkward angle (for me), conceals great, expensive, looks good. Downright painful when shooting magnums.
Pachmayr Renegade
Comfortable to shoot, large enough for a good purchase, conceals well despite larger size. This is the grip I ended up going with, very happy with it.