I use Voc Align Project with a Mac Book Pro that has a 2.2 Ghz Intel Core 2 Duo processor and 4 GB of RAM. I use it in Pro Tools LE 7.4 and have also used it a lot in Pro Tools HD and I've never had a problem with this plug-in on either system. I run Pro Tools LE with a Digi 002R audio interface. I am able to use this for exactly what I need to and what it is made to do - sync up vocals.
I've been using Voc Align for about two years. It is a convenient and easy way to tighten up layered vocal parts. It also works well when aligning instruments that need to be synced, but it is made for syncing vocals and is best at doing this. It usually sounds smooth and since I only use it on backing vocals, it is often hard to hear any flaws while it is in the mix. I've never used any other type of vocal aligning software, so I'm not sure how this compares to other plug-ins that are similar to this one. The price is reasonable and it will save you a lot of time if you have vocals that need to be tighter. I can say is this plug-in is easy to use and does everything that it claims to do!