Hi and welcome to JustAnswer! My name is ***** ***** I'll be happy to help you today.
If you'd like to reinstall System Mechanic, you can do so from the following link:
But if you want my honest opinion, then in answer to your second question, no I would not recommend System Mechanic. The truth is that, among tech professionals, these "optimizer" programs like System Mechanic are not taken seriously. There are several of them on the market and, while they typically will not HURT the computer, they don't really do much to help it either. Furthermore, on certain machines, they can even slow the computer down by taking up PC resources that should be going to other processes.
Of course it's up to you. If you feel like it has been helpful in the past, then you can certainly reinstall it from the link provided. But at $4.99/mo I would personally just save the money.
If you have any other questions on this, just let me know and I'll be happy to help you. And before leaving this page, please remember to use the rating box at the top to rate the answer at least 3 Stars/OK Service or better so that I receive credit for assisting you.