I've used Polowy Stone three times, once for bulk gravel for a paver project, then for some ledges or lintels or whatever they're called, and another time for slate for my patio.
I don't know anything about rocks except what I read about in D-I-Y projects. I asked for advice and they steered me in the right direction. The bulk gravel came the same day and was way cheaper than buying it by the bag from the home improvement stores. The ledges were something I could only get at Polowy and they even cut it down to the length I needed, which saved me renting a special saw. The slate was about the same price as concrete pavers from the home improvement stores but it's slate and looks very fancy. Plus, the slate or bluestone, I think it is, wasn't all beat up and scratched, so it looked good as soon as it was put down.
In short, I would recommend them because although I'm not a professional mason, they didn't mind answering questions, the delivery is fast and a fair price (it was $40 for two yards of gravel placed in my driveway, delivered that day, for me to haul up to the project area) and they have better, more professional supplies than I could find at Home Depot or Lowes' at a better price. Kinda "what's not to like"?
Also, they have some pretty interesting rocks and driftwood (at least I think it's driftwood) for decoration and lots of displays at their lot to give you ideas.