I haven't used it indoors yet, but I could. I split about seven cords every year over the winter (in the back yard after work each evening) and it is a good choice for me. I am paying about 25 cents per kilowatt hour for electric, works out to $3 or $4 worth of juice per cord split.
Compared to paying $150 to rent a gas powered splitter for two days and having to get all my splitting done right now I prefer the relaxed approach.
diameter (16" length) birch rounds with my electric splitter at 20 below no problem. Birch does split a heck of a lot easier than oak; and every species I have ever split splits easier the colder it is.