jay did you get your merlin today and have you set it up? is it better than what you were using previous? what is tds on output good? 
regards
ok paul here is the update
with the help of stuart from skypole i managed to get it up and running,
my tds from the tap is 275-300 (very high)
from the merlin it's reading 21 (i do have a di vessel in the van to polish)
i don't know if this will drop down after a few hours use?
to answer your question about previous system, i have always used a di tank but this was costing me £80 per month to use which is why i finally decided to get a simple ro.
now i have the best of both worlds because if i'm not in a rush i.e. when i return home from a days work i can refill my tank using the ro saving money on resin.
if on the otherhand i've had a busy day and need more water i can go home and refill instantly using the di tank setup which is installed in my shed along side the ro.
my mains pressure is not fantasic so therefore using the ro will take some time to fill my tank but that is not a problem as it can be doing this whilst i watch eastenders and big brother (sad git that i am)
all in all i am pleased with the merlin for it's price
(it does what it says on the tin)
Jay