Yes Bob they are, those tiny plastic gears are not intended to stand up to the vibrations in a glow powered airplane expecially tied to the throttle. Where they tend to fail in this application is from hard landings. Seems strange but these tend to strip those gears.

I understand the desire to use what you have but better using a little will power and get something more appropriate. Agine you certainly do not need to use a full standard size servo though on the throttles.

The advantages go beyond just lighter weight. It is particularly nice in a tight compartment to use a servo that physically is a little smaller. I have not used a 'standard' servos for throttle in many years.

Do not discount the HS -225 called the mighty mini, throttle dutys are a piece of cake for this one and I also use it for example on dual ailerons servo setups for a lot of airplanes up to what would be called sixty sized. heck even use that one for ailerons on many of my multe engine ships.

John