I never had a problem with the spied chain balance wise, I thought it was ugly in most illustrations, but I didn't find it imbalanced at all. A bit of a pain to run all the AoOs but overall not a better weapon than most. Now improved trip in 3.5 was imbalanced, in 3e it was balanced but kind of lame since as in 3.5 the skill component was not there, it should of been called improved muscle some one to the floor, because mechanically it sure didn't feel like a trip. If you are running a humanoid-centric opposition in your campaign it may be unbalanced because its strong suit is showing up all the time. Still people were devastating with more damage focussed weapons, though I did stick to 3e in many regards including improved crit, and keen stacking.