You’ll need to define “good” and “worth it”. At 10, your player is very young. Are you trying to build skill? Love for the game? Fun? And how much will make you happy?
Here are the similarities and differences:
Instruction:
MVSA: the beginner levels play newcomb. It’s not volleyball, but a precursor to volleyball. It helps with throwing mechanics and eye/ hand coordination. Instruction is on a set curriculum and it is mainly carried out by parent volunteers. There is a coach who knows about volleyball but that coach is working between 2-3 teams each practice. The parent volunteer may not know anything about volleyball…
Gaithersburg rec: the instruction by team is going to vary wildly. This is because it’s mainly staffed by volunteers. You’ll have some good folks like Coach Juan who typically coaches there in the fall (look up bears vc- he’s also varsity coach at CEDJDS) but most are parent volunteers. You can request a specific coach and team when you sign up. Some teams have been together for a bit and others are placed by the staff office. If you are going this route, your kid will have more fun if they are placed with someone they know, eg entire teams are made up of people from certain schools.
Learnings:
Neither one of these experiences will prepare you for club play even at the u10 or u11 level. It’s really meant for exposure, interest, etc.
If that is what you want, you would be much better off going to a more technical fall season / clinic. I’ve spoken to folks who had a good experience at RVA, Bethesda Volleyball Academy and Metro for this age group. A few clubs are opening up new experiences for this fall so you can try that out too.