Got my silver Sigelei 75W TC for 37$ with free shipping from them a week before last. Ordered late Saturday they shipped early Monday. It seems that I received the newest version of this device so their stock is fairly fresh.
The reason it's so cheap is because as part of their marketing strategy they are selling everything (all hardware) for cost until they lose 1,000,00$! Kinda ridiculous but it seems to be working. So, yeah they're legit, their stock seems to be fresh so if your item has multiple versions you might even get the newest one (holding down the power button and inserting my battery seems that it's displaying a date, 20150826, and I assume this must be the firmware release date from the factory).
Couldn't be happier with them, other people are selling this device for 60-75$.