Ernie,

The "Opto" version of the ESC means that the final driver stage is optically isolated from the previous stage circuitry. This has the advantage of noise immunity between the motor pulses and the ESC lines going to the receiver. On higher powered models, the suppression of noise is usually a good thing.

When you use greater than 10 cells NiCd or 3 cells Lithium, most ESCs will not longer have a BEC function. Note that the BEC version of the Jeti 40 amp ESC only allows 6 to 12 NiCds or NiMH or 2 to 3 Lithium cells. The Opto version allows 6 to 16 NiCds or NiMH or 2 to 6 Lithium cells.

The choice of which one to use depends upon the plane and motor size. For smaller planes using 2-3 Lithium cell packs, use the BEC version as it is simpler to use and lighter without the need for a seperate receiver battery.

Regards.