Benchmarks - HD Record
HD Video Record - 720p HD stream, 256kB writes
HD Video Play & Record - 1 playback, 1 record simultaneously
2x HD Video Play & 2x Record - 2 playback, 2 record simultaneously
The Thecus N5550 ships with 2GB of DDR3 RAM and the QNAP only ships with 1GB. Again we see the Thecus perform really well. The NAS slows a bit in some of the tests at RAID 5, mainly when recording and playing back data at the same time.
I wouldn't say it's a double the price / performance reduction.