Catalyzers are interesting guns that can let a player take a monster down to 0 hp in an instant (with setup time). This is a useful mechanic when having to deal with silkwings or menders.
These guns can turn an enemy into a walking (crawling or sliding) Bomb capable of dealing high damage to anything nearby, and with an amazingly short charge time this gun can set up quickly.
This all sounds so good, so why isn't anyone using them?
The answer inconsiderate teammates.
Suppose you are trying to setup a slime to lead in to the rest and blow them all up, then some striker nut comes up and nukes it with their Acheron. There goes all that work, planning and preparation down the drain. The bombers and gunners you get teamed with seem to only care about spamming Nitronomes and Polaris attacks, and soon you are reduced to spamming your regular attack in hopes that this damage can make up for the fact that your charge attacks can’t seem to be of any help to your team.
My general respons to trying to work with uncooperative players like this can be summed up in a few words....
http://wiki.teamfortress.com/w/images/2/2e/Demoman_autodejectedtie04.wav...
Happens with shard bombs and pepperbox too. No point using them unless others are too. Then people complain why isn't anyone using these weapons.