I've looked at the reviews for REN BB Satin, and almost all are 5-star. Next time I'm in M&S I'm going to test it. Last time I was in M&S I tried Stila BB and I loved it, but there are three options as opposed to just one in REN BB Satin.
i got some of the REN BB Satin to try also hen i was in M&S
i brought a little pot with me and asked for permission to take some home from the tester
i find colour matching on a hand/arm is not very accurate
and no natural light in the shop doesn't help
and it is hard to tell the proper texture without wearing it on your face
and also what it looks like after a few hours of wear ...
i have a draw full of bb creams and foundations which are not quite right
so i am not buying another one until i have tried and tested it a couple of times on my face
hence i come armed with little tester pots when out shopping
and explain the above ..and not have had anyone be less than happy for me to try some that way
currentlly quite impressed with the new L'Oreal Sculpt base
but as a natural nearly invisable foundation colour adjusting foundation
(i don't go in for all that contouring lark)
http://www.loreal-paris.co.uk/make-up/face/sculpting/infallible-sculpt-base
cheap as chips too
the other one i keep hearing really good things about is the Bourjois Healthy mix serum foundation
also one that looks really natural
and for that draw full of bb, cc or foundation creams that are just not quite right
a drop of facial oil or serum mixed in seems to improve them until i find 'the one'