If you did downs too ( which you don't and wont)
If you wanted to work faster with better quality (not possible because you know)
If you were serious about making money and wanted your round to grow dramatically
If you can purify water pre van so that you could do away with the DI onboard, then and only then.
And assuming you already have a pump and a variflow, then...
SSSHH,,, But you could do worse than buy a Rinnai REU 58.(£249inc vat) and from this all things would follow.