Two-pack is nasty stuff. It has cyanide in it! That is why it's illegal to DIY it in the UK, and if you want a really good paint job, then you have to get a spray shop to do it in full breathing gear.
Problems can also occur when spraying cellulose over a two-packed paint job to touch it up. It can bubble up and flake off.
If you want an expensive shine get a two-pack job done, if you want to touch it up use cellulose at home.