I prefer the HKS over the other two for just toting around. I haven't used the Buffer Tech. but I've got a bunch of the CompIII's for K and L frames which are very similar. I've also used/have some Safari CompI and II.
All except the HKS are apt to "unload" on you, and the CompIII's are a bit long for carrying in a pocket. I too have a SP-101 that I won at the NRA nationals that I gave to my wife (she took a real shine to it when I brought it home!!) I keep some HKS's loaded with Magnums in the console of her car,and the gun loaded w/USA .38spl+P 125hp as she despises recoil of magnums.
I've got about 12 loose rounds in the console of my Jeep where a couple of compII's have unloaded while shuffling #%&* around in the console looking for the key to the range gate.
Just my experience, YMMV
Yes the J-frame loaders will work, but the Magnum rounds can require a little manipulation to go into cylinder. Another reason I favor the HKS's.
I've used speed strips through the years. I quit using them as soon as my agency allowed us to carry speed loaders. (carried a speed loader in my jacket pocket though!) The Safariland compII's we carried in over the belt pouches would unload about once a shift, usually when I was leaning over the side of a boat or bed of a pickup. We soon went to HKS's and had no problems. However for speed, the compIII's and BufferTech's have no peer. (much easier to refill than moon clips too). In NRA PPC, about all you see are CompIII's and some Buffer Tech's are beginning to show up.