Recently I have come across a few ARFs labelled as .25 size (and other engine sizes) only to find after looking at them closely that they are made for exclusively for electric power. A lot of work would be needed to convert them to glow. I find this to be a bit misleading. Some time ago, electrics used to be labelled as 'speed 400 size" or "speed 600" as well as a suitable number of cells, but I guess with all the brushless motors and Li-Po batteries available and no standardisation within the industry, it's just easier to call a plane by the equivalent size of glow engine that would fly it.
I've read a few posts regarding electric setups and I just can't follow all the numbers. It seems that people specify a particular brand and model of motor, type and number and capacity of cells in the battery, capacity of the speed controller and prop size. Given all the possible combinations of these components available, I can see why they call it a .25 size.