Hmmm . . . .
Fly-sky :
none in stock,
6 Channel :- two reviews, one of which had his transmitter fail after 2 weeks
4 Channel no reviews at all
Radiolink :
10+in stock
4 channel 119 reviews (mostly 5 stars)
6 channel 17 reviews (again mostly 5 stars)
I also write as a happy RadioLink user with no problems (2 Tx, 6 Rx), though I note that the 4-channel Radiolink also has one 2-star and three 1-star reviews - typically from people whose radios failed. Buying cheap Chinese means that quality control is always going to be an issue, as ACTion remarks...
It's unsurprising to have few reviews for a new system, and the fact that none are in stock points to a very competitive price. So I still suspect that the FlySkys are very similar to the Radiolinks, and very good value if you want to experiment. Assuming you don't mind waiting.
Myself, I'm not going to buy any of the cheap FlySkys - because I'm fine with the Radiolinks. I would have bought one if I wanted to experiment with 2.4Ghz cheaply. But I
am tempted by the £55 9-channel FlySky FSTh9X/B . For what it offers, I think it's a better bargain than the cheap ones...