Hi Eurycerus,
Yes … I think highly of them and their knowledge and experience and I have had some great conversations with Steven there. None of their mattresses have any weak links in terms of their design or the quality of their materials.
A forum search on European Sleepworks will bring up more information and feedback about them and they are also one of the better options and possibilities in and around the San Francisco /Oakland area I’m aware of in post #2 here. The San Jose list in post #2 here also includes some of the better options in the San Jose and southern East Bay area. They would certainly be well worth a visit.
Mattress warranties are usually more about marketing than anything else and the quality and durability of the materials would be much more important to me than the length of the warranty because warranties don’t cover the main reasons that a mattress needs to be replaced … only defects in the mattress which tend to happen early in the life of a mattress (see post #174 here).
The importance of a return or exchange policy would depend on the results of your testing and how confident you are that a mattress is a good match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences). Return and exchange policies are built into the price of a mattress and the people who don’t return or exchange a mattress pay for the ones who do. In the case of the European Sleepworks mattresses … their component design has the option to customize and fine tune their mattresses both before and after a purchase which can certainly be helpful if your sleeping experience indicates that you need to change the comfort/pressure relief or support/alignment of the mattress. In other words … it would depend on the parts of your personal value equation that were most important to you and your confidence in your choice.
Return or exchange policies have little to nothing to do with the quality of a mattress or the knowledge, experience, or service of a mattress store. It’s just one part of “value” and cost that may be more important to some and less important to others.
I’m looking forward to your feedback if you decide to go there and visit them 
Phoenix