As mentioned many times before...
I had no converter in my 13. I used a schumacher charger set up like your friends and got along just fine.
Charger charges battery, battery runs 12v stuff while being replenished by charger. No muss, no fuss, no bother.
I use solar
when off the grid.
My 17 has a converter that also has a distribution panel. The breaker for the converter function has been set to off permanently, and I hard wired in a similar charger. (After disconnecting the charge line from the converter, of course).
I still seem to get along fine.
The converter has "eaten" one of my LED domes and plays havoc with my TV/CD player. I flipped the breaker on in Oregon as I was running all my lights
at once during trailer tours. Folks were interested in them. I have no proof, as I didn't investigate to closely, but I have my suspicions about the charger with the converter contributing to a VERY premature death of a brand new battery. I used the converter to charge for a bit before I installed the Schumacher.
As soon as I get motivated to build a new distribution panel, the big heavy thing will get pulled out and I will have more storage where it is.
Note that this works for me as all my stuff is low draw.. LEDs, cold cathodes etc. This may not work for those that like to use thier incandescents or other heavy draw items, such as inverted TVs. The charger wouldn't keep up.