That page describes a commercial implimentation of the sound drivers included in most Linux installations. From the page, the benefits of spending $15-30 are:
* Support for Linux on x86, Linux on AMD64 and Linux on Alpha Processor
* Commercial grade product for Linux backed by full technical support and support for the latest Linux kernels.
* A user friendly GUI (curses based) to configure the soundcard!
* No more guessing soundcard kernel parameters and no need to recompile your kernel to add sound support!
* Support for PnP (plug and play) sound cards!
* Support for certain sound cards with proprietary programming info. Note: such cards will not be supported in OSS/Free.
* Autodetection of certain soundcards and manual configuration ability to change soundcard parameters on the fly.
* Full Duplex Support for Creative Labs Sound Blaster 16 / AWE32 / AWE64
If you think those are worth the money, then go for it.
The regular drivers should work, though, and are not time-limited in any way. In particular, if your sound card works now, I would recomend against buying it.