Don't worry about more pics...I knew from the first one.
It's a Rhino pleco (See my avatar for a more colorful one). The average max size is around 12-14 inches... however there has been some on here that have gotten them up to 16inches.
http://www.planetcatfish.com/catelog/species.php?species_id=80
As with any pleco... there is some risk of sucking on other fish. The trick is too keep them well fed.
For me, I'd take the pleco over the rays but for you, I'd say pass on this one(since you didn't raise it...you don't know how it will behave).