They are both great rels, but it's like comparing apples and oranges, first
off there is no 251 TE, but the 201 will suffice. The TE has 10 ball
bearings and a roller bearing, the 251 has 2 and a roller bearing. The TE
has a completely different side case on the handle side with a completely
different, beefier and more efficient gear set, and the other features
mentioned before. That said I'd had a 251 for about 10 years or better and
it's never given me a lick of problems in fresh or sal****er. It is reported
that this series of reels are the first reels designed by Shimano where the
reel's design was of maximum concern and than the bean counters had to worry
about how much to charge for them.