I ran the L21 for a week now, so far so good. Hash rate seems to be stable at 480-500 M/s (not 550 as advertised) i'm no sure if the pool affects the hash rate or not ( i'm using litecoin.org ).
It is running very loud which is not considering to let it sit in your house. The miner is running cool ( i guess the high speed fan make it running cool ).
Some people say it's way overpriced but L3+ is $2000 right now at bitmain.com, i'm not sure if this is still true  . Shipment speed and customer service at Hyperbit are ways better than Bitmain too.

I'm trying to mine with other pools to see if the hash rate increase, if so may be i would get few more.