I wasn't the biggest fan of Strike Suit Zero, mostly due to many shortcomings I had problems with (read my review if you'd like to know more). However, and to my surprise, Strike Suit Infinity is such a nice game, I'd say it's even better than SSZ, because they fixed so many problems I felt the original had.
-unlike Zero, Infinity is just there as an arcade kinda game. You ascend higher into the levels and stay alive, shooting as many enemies as you can. mostly for points
-you can hire escorts, from tiny ships to massive frigates, and they'll actively help you as long as you help them
-you can upgrade both them and your ship thanks to credits you earn throughout the stages
-strike suit mode is so sweet, and they actuallly make it more vital to the gameplay by giving you the ability to greatly extend how much you get to use it. Plus, right off the bat you get a good selection of strike suits with different abilities, since you can unlock 1 pretty early, and the other is right behind it.
-overall a light and fun experience
Even though I still find issue with the controls, the game is far more lenient in intense firefights, but there's still challenge. They really did improve the core of the game. So yeah, buy it if you can, on sale or no. I recommend it regardless.