I've now seen enough reports of good luck with them that I feel comfortable recommending them. Check your existing card's manual to see if it supports this. I can make no guarantees about support from other cards. Whether drivers for Creative products will continue to improve is another matter, though. They're already well behind the competition in terms of features such as full-duplex support.
Sound quality is reputed to be variable, with older models being so-so and newer models pretty good.
Unfortunately, because these bargain boards are often generic, I can't offer specific contact information at this time. Note that the Crystal boards, on average, will probably produce slightly better sound than the ESS boards. Otherwise, should work fine and provide superior compatibility when running DOS games. You'll have to pay the registration fee for the Manley drivers, though, effectively raising the cost of the board. Be sure you have at least 1MB of RAM on any GUS board you get, and preferably 2MB or more.