The most recent jet that I finished last month, I only have the UAT as the filter. I have one filter on the fuel pump can after the can pump and prior to filling the jet. So, two filters prior to being burned. The previous jet, I have an additional filter prior to filling the UAT. So, 3 filters prior to being burned. I quit using an inline filter after the fuel pump/valve several years ago. The main reason is to eliminate another restriction and leaking point. The only reason to have the filter after the onboard fuel pump and valve, is the internal failure of the pump side of the electric fuel pump. Seems to be very rare, if never. Reo is one of the few that I have ever heard of having problems, so not impossible. There is another reason to have a filter after the pump/valve is for warranty reasons, so read the fine print. Manufacturers will take the most conservative approach. The UAT being the main fuel system filter; I personally feel to be enough filtration. The new cylinder UAT have the micro stone filter when the fuel is leaving the UAT. Extremely fine filter. The micro bag filter in the BVM and other same style UAT filters is also a very fine micro filter. Let’s also remember that the jet fuel truck has additional filters. We as pilots are likely to contaminate the fuel when transferring from one 5 gallon can to the main fuel pump can. We are our own worse enemies.
The situation of creating onboard microorganisms can happen if after flying, the fuel isn’t drained. And even if you drain the fuel, not all of it is pumped out. Here in Florida and other gulf states, during the summer, we are usually very humid. The fuel left onboard could create condensation if you store your jets in the house in a/c. The water is what is needed to grow the bugs. If so, chances are the UAT filter will clog and will either not start, or a flame out. Hopefully not on TO.
I do think that we over filter the fuel.

Take care! Dan