Hi lewis,
I purchased a ASI533 late last year and enjoy using it.
I can't give any other camera comparison comments as this is my first dedicated astro camera after using a dslr.
Still coming to grips with operating everything - I'm a slow learner
I did consider a mono camera but was concerned about using filters plus the additional cost.
It didn't come with dual band filters and like you I am considering purchasing a L-extreme.
I attach it to a SW Esprit 80mm on a HEQ5 mount.
cheers