Yeah, when I was reviewing MS, I came to the same conclusion: the relay
board is a complication -- perhaps an unnecessary one.

Since the 'bishi already HAD 3? relays <the old 'vacuum computer'>
that would go unused, I didn't see a reason/need for it. Using the
existing relays held a lot of packaging advantages, and allowed me to
fully use the existing harness, and its weatherproof connectors.

Std relays are easier to troubleshoot and <spontaneously, i.e. NAPA> replace,
I think. I only had to add <pull> three add'l wires to the existing to make the whole
thing work!

If I were adapting to a car that didn't already HAVE an ECU, it would have
made things easier having the board.

My 914 had such a board; ancient bosch printed circuits which fail from
heat/moisture, with relay sockets atop. It goes in the heap, replaced
by the MS board.

So, the "relay board" really serves TWO purposes;

- Makes installation of new features much
easier than re-soldering the DB37 <messy> on a full harness, IN THE CAR;
- and allows higher current controls where needed <i.e. fuel pump>.

My use of the harness adapter accomplishes the first objective, without
the relay board -- and without REQUIRING it when it isn't useful or needed...
such as, when the target car already HAS a bunch of relays that are no
longer used. Or, adapting sensors, where you'd like to MINIMIZE the number of joints
to corrode and change values, like TPS and TEMP.

YMMV, as you're doing some special things. But, I thought the
distinction about 'dual function' important enough to post.

HTH.