Common? Probably is, but maybe half the experienced modelers like inline filters and half don't. Depends if the modeler uses tubing that fits to begin with. The right size won't come off and doesn't need help staying on. And a lot of modelers know how to keep filters screwed tight and put fuel tubing on. Plus, having a filter near the carb often improves engine runs. Truth is, learning what fits what is one of the things beginners have to accomplish.

Are inline filters recommended for beginners? The ones who are apt to not maintenance their stuff over time and can't get the hang of putting tubing on that stays should probably keep things as simple as possible. The use of fuel filters is a sensible thing to do. It just depends on your own attitude and capability where you use them.

They can actually serve a very useful purpose. See the filter on the deliver line to the carb? That model has a simple two-line tank. I use the delivery line as the fill line. The line to the filter from the tank is disconnected to fill the tank. It never comes loose and doesn't come close to needing zip ties or whatever. The tubing fits the filter nipple and the nipple is perfectly adequate in length. Component selection is one skill beginners will acquire over time. That filter has been in use since the 80s. It's never had a hose come loose. And it's been cleaned out too many times to count. Didn't have anything in it most times. And I had no idea how anything gets into it the times I've found stuff. Still, it's worth having there. I started using inline filters back in the 60s. They've never been a problem of any kind. Been useful where they can be used as a "gas cap" and have trapped stuff as well. I also use a filter in my fuel delivery system. But stuff still shows up in the inline at the carb. Who knows how it gets there. Who cares, if they have a filter that stops it.