I use the same one I fly stunt with.  Have fun,  DOC Holliday

Aw shucks, it 'twarn't nuttin.  I needed the handle for my own models, and Eric up and kitted it!

Anyway, the handle is currently availible in 3 sizes, original, +10 and +25.  My current preference for 1/2A is the +10 as it allows a better grip.  I really did cut the original a bit too close, even for my small hands.  Anyway, the +25 is great for up to .35 models, and if you reinforced the main panels with fiberglass, you could fly anything.

The expo function was intended to tame un-flapped models, and I have found that with flaps, you need to reshape the inserts to reduce the expo.  A full radius is the first step, then you can go all the way down to a point to make the handle completely conventional.  Since the inserts are pretty simple 1/8" ply, it is easy to make a vareity of shapes and widths to perfectly tune in your model.

I don't keep up with Eric's catalog, I am sure he will answer your questions with an e-mail to Eric1@rsmdistribution.com  .  I expect the .15 size is the +25.  He may have made the +10 standard by now.  I will have to ask him what is the status so I know.