I am currently using a Logitech T620. No visible buttons like the magic mouse. It uses Logitech's unisync (I think) multi devise dongal. This mouse has ultra smooth Internet browser scrolling and feels Ok in the hand. The magic mouse is much heavier and has a better quality 'click', but the T620 does a nice job for the price.
I can't think of any non-game-related scenarios where you might need to both left and right click at the same time.
Hold Right Click to aim, press left click to shoot. You can't do that with these mice.
That's game related. I said I can't think of anything not related to games that requires both clicks at the same time.
Various design programs would have the user holding both mouse buttons to pan the work area in absence of a mouse wheel or middle mouse button.
But that's the nice thing about these touch mice, scrolling is the most perfect thing on them with a swipe on the panel. At least with a Magic Mouse on OS X, you can click and scroll at the same time. I've done so many times while highlighting many files or a lot of text.
I use a Razer naga epic. I own 2 nagas for me and my wife's computer and love them to bits. My friends have had good experiences with mice from corsair, mionix and logitech's gaming series. I definitely can say the Razer naga is the most comfortable mouse I've ever owned.
Actually, I would recommend Logitech T630 (successor to T620). I think it's the closest you will find as an alternative to magic mouse.