Would it be a terribly big deal to go with the stock combination valve for my disc/drum setup?

I am only wondering because the Wilwood valve will require me to buy additional tools: a flaring tool and a line cutter in order to use my existing brand new lines with that valve.

If I really need one, I may just go back to the original plan and use an inline valve on my rear brake line (which will still require me to cut and flare, but not to cut and flare brand new lines).