I have been doing some research on different brands of hardwood and found an impressive product from Germany called Pollmeier. It's made of European Beech and seems to be of high quality. Just one problem, I don't know of anyone who has used the product and thus have no idea how it holds up over time.

Does anyone have any experience with Pollmeier?

We have used it a few times, no significant problems.
One word of caution but it regards beech in general, not the manufacturer.
Beech is probably the most sensitive wood to fluctuations in humidity levels. You best advise the client to make sure they have good humidity controls in place to maintain a very stable environment for the floor.

I recall doing a floor years ago. Originally, it was to be a natural red oak. But when the shipment arrived, it deviated so much from the sample that the customer refused the shipment and wanted another type of wood. I showed her a Lauzon solid Beech floor and she loved it. It cost me a little less as well. It wasn't until later I learned Beech wood wasn't very stable. But I guess it was fine in her home as I never heard back. No news is good news, right?