Pros:
It's a very simple thing, with few moving parts.
When it works good, it works good.
Cons:
Can't run WOT at high airspeeds due to the turbulent airflow generated in Van's FAB causing problems with even fuel distribution. That is, you'll give up the ram-air MP benefit of the Van's setup. Van tried to make the Ellison TBI work years ago, and gave up (as I recall). I've tried various (internal) changes to the FAB with little/no improvement.
Very susceptible to vapor lock / fuel vaporization, on the ground and in the air. I live in Maine... (multiple iterations of fuel line routing / shielding).
Fussy with mixture settings...too rich is way too rich...too lean is way too lean...hardly any paint left on the red knob...
Personal Observations:
The Ellison people haven't been very friendly or helpful, a characteristic that some other (non RV) TBI users have also experienced. (Not that I'm all sweetness and light)
If they worked so well, how come more of the RV nation don't run 'em? They've been pretty popular in the Canard-community, but, as you know, the air induction system is very different.
I don't believe there's anything wrong specifically with the Ellison TBI, it's just not well-suited to the RV design.
Does anyone else remember when Van tried to give them a go?