a lot of people train them this way because they are a small muscle group and they do get worked with most other body parts. if one has the time i think it is a very effective way to work them. i have a gurly arm day but im not trying to grow my arms any bigger, just want to get them leaned out.
i do think that many people overtrain bis and tris. because they do get a lot of work with other body parts they dont need 10 different exercises to work them. i have definately become a fan of the less is more when it comes to bis and tris. 2-3 exercises of 3-4 working sets with 12-20 rep range.
but as in many things, there is more than one way to skin the cat and what works well for one might not work at all for the next.
i think you should try it for a 6-8 week cycle and see how it benefits you. take pics and measurements so you dont go by feel but have actual proof.
the other benefit is it gives your tendons and ligaments more days to rest and recover.
have a wonderful day!