When you have legislation restricting the number of pistols allowed, conversion units are a real benifit. Smith & Wesson do not see the need at present as they are pushing their M&P22's made for them. However the M&P line is ideal for this with a .40 purchase and then add .357 Sig and 9x19mm barrels, you have 3 calibres BUT practice is still not as cheap as having a .22Rimfire conversion unit. I'd have one each for my M&P's FS & PRO 5" models. Come on SMITH there is sufficient demand for these conversion units.