My son (who's now almost seven months) has been EC'd strictly on the toilet (sitting facing the wall) and doesn't know what to do when I cue him on a potty. The problem though is that he's getting big and not only is he heavy to hold, but he pushes off with his feet (which can knock me right over backwards if I'm not careful).
I've been careful to let him off as soon as he gives me the signal that he doesn't want to sit there, but often that ends up with a miss. We've had so many misses in this manner, that catches during the day (the first morning pee/poop is always in the toilet) are hard to get.
He's been crawling since 4.5 months (army crawled for a few weeks, then full hands/knees since 5+ months), so I'm sure he just wants to go. He WILL sit still for a few seconds if I sit him on the baby bjorn, but it won't be long before he won't (he already knows he can throw himself off, he's just not quite big enough yet).
I like to continue using the toilet (I've tried a reducer and he will sit (albeit trying to grab the toilet paper the whole time), but I won't get a catch until I remove the reducer and flip him around.