I don't believe it's really lower end .. not for bridgestone. It would have been only a few models below their entry level road racer the 600 those years. It may not be built for the same application but still usable as a racer, I'm sure. I have a 550 -which seems to fill the entry level slot vacated by the 600 series which I guess was dropped when the RB models began- in metallic blue
nice paint
weighs about 24 pounds and is pretty fast ..but a little "skittish"
The saddle on mine was different but still sucked. I'd definitely change that even if only to a new cheap saddle off ebay for $15.
A better bike presented itself this winter that was my true size -a 54cm Stowe opposed to the 56cm Bridgestone
but still, for the couple hundred miles I got to ride it it was pretty cool.