Well, the quick delivery certainly must have been a pleasant surprise! It sounds like they handled everything well, eg, packaging, responsiveness to your requests, turn around time, mounting, print quality, etc. That's great.
I think that one of the important lessons to be learned from your experience is that starting with an image that is very small (in pixel dimensions) by everyone's reckoning can be just fine so long as the owner's expectations for sharpness are realistic (as yours were).
Printing companies have progressed well past the point where the customer had to worry about obvious pixelation in the final product.
Now, so long as the customer realizes that one can't expect to inspect the large print from 6 inches away and see every pore on the subject's skin when this wasn't even possible on the original when viewed from close-up. Instead, the expectation must be that the viewer will look at the large print from several feet away, or even from across the room, and it should look more or less the same to them as if one was looking at the small original from a much closer distance. It's surprising how many people, particularly, pixel-peeping photographers simply don't "get" this.
In other words, Krispy, your instincts were right on the mark!
The next time you have some prints made, you may want to further improve on what was done here and add a tiny bit of texture or noise that remains fairly sharp at the final print size. This is what lots of advertising agencies do when they are making large display posters because it gives the viewer's eyes something sharp to focus on. It will be interesting to see if you think this is an improvement, as well.
Gotta run.
Congrats on your new prints.
Cheers,
Tom M
PS - Thanks for taking and posting all those pix. They were very helpful.