Not my cup of tea. Prefilters are small and are not conventional, so you need to buy replacements from RO Buddie. Go for a conventional RO unit and get one with DI. Spectrapure sells refurbished units for a good price.
I would get an BRS 4 Stage, far better. The 4 stage will pay for its self in less than a year due to low cost filter replacements alone and to say nothing of the fact BRS ships its systems with every fitting or adapter you could possibly need to get it going and hooked up easily. Don’t be a dummy, get a BRS. Lol
This could literally be the make or break piece. It is that vital and certainly not an area you want to go “cheap”. Starting with the best water and doing water changes is the best way to solve most any problem in a reef tank. However using a questionable unit will cause severe heart ache long term.BRS filters are not cheap, low cost maybe but it’s quality and does the job you need it to do. As time goes you can also upgrade this unit easily. I bought the same basic 4 stage and now have 6 stage, Dual RO Water Saver, boost pump, and float valve that automatically fills my 100g mixing station. I have had to change a filter yet, just the DI stages twice in 3 years. I make around ~300-400 gallons a month on average.