Legacy Mode Performance
I ran a quick check to see how the 1522 behaved with "legacy" clients. I used the Intel 2915abg internal mini-PCI adapter in my notebook and tested with the 1522 set to 2.4 GHz and 5 GHz 20 MHz bandwidth modes. The notebook was about 10 feet away from the 1522 in the same room and no other networks were in operation.
Figure 20 shows that the 1522 provided just shy of 19 Mbps, which is a bit below the mid-20 Mbps performance that I would have expected.
Figure 20: 11a client performance
But when I switched the 1522 to 2.4 GHz mode and reran the tests, I got the surprise shown in Figure 21! 7.5 Mbps is very poor performance; about a third of what I should have gotten. I also tried a second notebook with an internal adapter based on Atheros' AR5001X+ chipset and got total throughput of 12.5 Mbps (9.5 Up, 3 Down).
Figure 21: 11g client performance
This, plus the uplink results and other things I saw during my 2.4 GHz band tests tells me that D-Link and Ralink have some performance tuning work to do in that band.
Security Mode Performance
Since I previously found two Ralink based draft 11n routers that did not exhibit the severe throughput penalty in WEP and WPA/TKIP modes (the Belkin N Wireless Router and Edimax BR6504n), I almost skipped testing the 1522. Figure 22 shows that it's a good thing that I didn't!
Figure 22: Wireless security mode performance comparison
For some reason, it looks like the security mode throughput optimization Ralink provides in the other products is not present in the 1522. So use WPA2 AES when enabling security or suffer the (throughput) consequences!
The good news is that the DAP-1522 can add dual-band draft 11n to your existing router for about $100. The bad news is that its 2.4 GHz operation draft 11n performance seems unstable and it may really stink at supporting legacy 11b/g clients. And while its 5 GHz performance seems like it has had more attention than the 2.4 GHz, the 2T2R radio won't deliver as high a throughput as you'll get with more expensive three-antenna 5GHz products.
Still, there aren't many other ways that you can get access to the relatively clear 5 GHz Wi-Fi airwaves for as little money. While performance won't compare to the more expensive options, you won't feel as bad replacing it when better options come along. Just set it to the 5GHz band and keep using your current router's 11b/g radio.