we considered it, but got dismissed as a bit too techie - similar to Vector.

vector is perfect.

"too techie" is only too techie if you are too techie otherwise it is just an appropriate name

I am very glad you are moving away from riot. makes it easier to talk about.

A subtle nod to cryptography, I love it. If not Factor, Prime? Oh, perhaps not :-)

Comma.ai is commandeering "prime", why not Matrix clients?!

Factoring is the point at which a lot of people start truly hating math. As in going from having a weakly negative or even somewhat positive opinion of the field to hating it. I'd avoid the name.