The only downside I've run into when joining cords like that for use with
a moving tool (mower) is that the "lump" in the middle of the cords tends
to hang up on things far more often than a full length cord will.

Don't know how things are at your house, but at mine, it's a hard and fast
rule that if there is ANYTHING for a cord to hang up on, that cord will seek
it out, and not come unhung no matter how many times you flip the cord. You
must physically walk all the way back and free it from this 1/2" protrusion
or tiny tiny stub of a root.