I want to set up an 802.11a-only WLAN, but should I buy 11a-only products?
Dual-band products are probably a better choice. 11a-only products are quitescarce, pretty pricey if you find them, and probably use the obsoletedfirst-gen Atheros 11a AP chipset, which you don't want because of its inferior performance. We also recommend not buying 11a-only client cards for the same reason.
Dual-band products are finally making a comeback in draft 802.11n products. They will be pricey (around $300) at first for wireless routers capable of operating in the 2.4 and 5 GHz bands at the same time. But the price will come down pretty quickly.