I've only ever tried 1 slab of Express and they left brass colour all over the breech face on my Beretta SP1 I had at the time.
Nothing wrong with that as such I suppose, but it never happened with any other shell and it just made me think/feel they we're cheaply put together so I lost confidence in them.
Add to this they seemed a bit pricey, Ive not tried them since.
Iggy.