Is urethane-based grout worth the cost for bathroom tile?
I, and many tile pros, aren't fans of the pre-mixed urethane grouts. Again, they're newer products. There's two downsides to the urethane grouts I looked at. The first is that the dry time before water exposure is something like seven days ... again, this is the last time I looked at it, and that might have changed. The urethane grouts are supposedly easy to clean, HOWEVER, every tile guy I've talked to has said it's not a product for newbies. 

I haven't worked with them personally, because my go-to is Spectralock by Laticrete. Spectralock is an epoxy grout, and can be had at Lowe's or through your tile supplier. You mix two parts goo with one part colored sand, and you get a very consistent and easy to apply grout. You have to pay careful attention to the setup time and the cleaning instructions, though, because they will leave a haze on your tile as the epoxy sets up if you don't clean promptly, and it sets up quickly.