I just got some Orlite mags and think I'm gon-a like them.
They work great and are ligher than my other mags but do they really last or will I need to buy new mags sooner than with steel or GI mags

It's unlikely that you'll ever need to replace mags in your lifetime, any mag.  If you don't keep them loaded all the time, cycled the loaded ones, load a few rounds down, and keep the mags clean they should last forever.

The Orlite mags will probably last longer than the steel (most of which are crap anyway) or the aluminum USGI mags because both of those can corrode.  

Orlites are good and they are cheap.  Not all of them drop free and some are a little hard to insert, but they last forever and are half the price of USGI.

Note:  I still buy USGI whenever I find a deal.

Have had my Orlites for about 12 years, and haven't lost one yet.  My only AR until recently was a Colt, and I never had a problem with fit.  I recently built up a heavy barrel on a Rock River lower, and had to shave some material off the rear ridge on some of the mags, and take some off of the ridges on the sides, to make them latch in the RR reciever. If yours fit your gun OK, enjoy.  [:D]