This tbh, good all round stuff, ive used it on gpu's, and chipset heatsinks, also has no curing time unlike as5 which takes a while to reach optimum.you should use mx2 anyway because it's non-conductive
MX-2 is probably the best performance for money paid on the market. Easy to work with as well.
I wouldn't be worried about the money part when it comes to thermal paste unless you're building like 10-15 PCs a day then you won't notice the few pounds difference in price between them.
MX3 is worth the extra if you're buying one. But obviously if you've got some mx2 left then there's not much need for buying a new tube unless you really need that 2-3c less.