Take a look at the photos in replay #22 in this link. They clearly show the difference between FTZ lugs and NSPA lugs. Note on the FTZ lugs, there is no visible seam on the edge of the lug. The Amazon seller I bought my first crimper from told me if there was a visible seam, they were not FTZ lugs. They took the crimper back to examine it but I didn't hear back from them.
I then bought a crimper through this site.
I spoke with GD a few times about the lugs I bought from them. They explained they use them with good results when making up custom cables but they do use a bench mounted crimper which may give them better control. That and they make a lot of crimps.
Probably with experience users can get by with the cheaper lugs but beginners or those of us who are doing our boat, then moving on to other projects, want to get the best results possible early in the learning curve. Having FTZ lugs just make sense.
I trust getting the lugs from SBO and Bay Marine Supply. And GD is still on my list for marine electric parts.
Maine Sail gave me real good prices on battery cable, a charger, alternator and some smaller parts. I always consider him also.