you can use any servo in the rc world with the 4pk, trust me. That thing is like an alienware gaming computer. The BLS servos are kinda overated I think, The better servos are digital coreless ones from futaba, JR is really good but expensive, but the titanium digital ones from Hitec are good too. Any of these are usually high quility. as for the digital, the 4pk has a seperate setting for that called HRS. This can only be used on digital servos ONLY. PPM or PCM are for analog servos.