That's the same one I use, it really is the most comfortable one I have found after trying a good number of them.
I remember not being able to use the scroll modifier as a back button as well (something else I struggle to live without) but looking more into it - it looks like that's either an incorrect memory or no longer true!
I've been tempted to try one of the Kensington offerings (one of my Logitechs has a dying button and I'll need to replace it soon) - have you tried the expert mouse or the slim blade? How do they compare to the Logitech?
I remember not being able to use the scroll modifier as a back button as well (something else I struggle to live without) but looking more into it - it looks like that's either an incorrect memory or no longer true!