Welcome to TFP. I wouldn't count on much October swimming, even with heat. The air is just too cold here to make it very attractive. Normally the same in the first half of May. You can get the water warm enough, but it's cold when you stand up or get out of the pool. My personal experience is that the heater is most beneficial in warming the pool a few extra degrees right in the middle of the season.
I assume you are referring to a heat pump and not a true electric.
Heat Pumps and Gas Heaters differ quite a bit in operation. Heat pumps aren't usually large enough to quickly heat a pool, so it's normal to run them all the time, or at least much of the time, to keep the pool warm. Large gas heaters can make a significant temperature difference overnight, so they are handy for warming the pool up for the weekend, although they can be used continuously as well. When comparing prices on the heaters, make sure you find out if you need to upgrade your home's gas line and meter. This can cost some money that may change the economics.
Some of it comes down to personal preference, but some years there isn't much swimming weather here after Labor Day. I have solar heat, and can usually hold my pool near 90 through September, but we may only swim once or twice after Labor Day except for an occasional dip for swimming laps.
If you have an unshaded southern or western roof exposure, consider solar heat. Far cheaper to operate and cheaper to install.