Is it boosted with a pump or straight from your tap ? if the latter do you happen to know what your mains pressure is ?
Asking because I used to have the old merlin but went to a 4040 soon after because of high waste and tds issues. Now I maybe selling my flat and the 4040 membrane needs replacing, thinking along the lines of the pentair again due to its size and portability as I may need a van mounted solution until I have new permanant living arrangements. Do you have experience of the old merlin ? is it improved in any way other than visually ?