RS500 or FS500, it's the same only different names (different countries, different names for the same products...)
These are rather cheep micro servo's:
Here are the specifications :
Dimensions: 29.0 x 13.5 x 29.5 mm
Mass/weight: 18.00 pond/g
Operating voltage: 4.8 - 6 Volts
Nominal voltage: 4.80 Volts Nominal voltage: 6.00 Volts
Torque: 20.00 Ncm Torque: 25.00 Ncm
Transit speed: 0.15 Sec/45° Transit speed: 0.10 Sec/45°
Small, fast, low-cost micro wing-mounting servo offering high torque; ideal for all applications where powerful control surface movements are required but space is tight. Ideal for wing-mounting, even in thin airfoils.

I do not trust these with those large control surfaces and tiny plastic gear. A torque of 20 Ncm is also not soo much, but that should be sufficient I guess. It's those fragile little gears that bothers me the most

What do you think, should I replace them with S3001's (I have a few of them waiting for a plane).
The servo's of the the rudder and elevator are build in the tail, I'm a little worried about the CG when I replace them