If the talon works for you with a Glock, it should work even better with a lighter gun...I tried the talon with my P7 but found the gun was too heavy to not use the belt for support..I have the high noon for my SP101...it works very well....again, I like the fact that the clip goes over my belt as opposed to clipping on the seam of my pants since it holds the weight better....but with a 642, I don't think that will be an issue...
My del fatti isp-dd is similar to the Alessi but the clip works over the pants or over the belt...the clip is also offset so not having it over the cylinder makes for a lower profile in the pants...