ive used resin only system cost a fortune,got a ro very cost effective get my tds reading down to 009 from about 360 but just invested in a elga two stage deionisers which regenerates the resin very expensive piece of kit brand new £3000 or more,but nomore resin to buy.I would go for a merlin and run it through a resin vessel cus your tds is low you may get nearly pure water on demand through it.
gaza