ive got a slate floor to grout and was wondering if it was worth having a go with one of silicone style grouting guns to save time cleaning off. Has anyone used these guns and are they effective?

Yes, I have and found it a pain to use, a single blockage can cause grout bubbling out everywhere. Have got some grout bags but have'nt needed to use yet IMO

cheers thought that might be the case ill grout as normal

Cant see the finish of the grout line being perfect without a swirl of a washboy sponge, in which case you may as well apply it normally as well!

I bought one for slate - customer requested large joints.
It was rubbish and is consigned to my "rubbish" section of the garage. Just work cleanly and grout as normal, or ideally use BAL temporary sealer - I keep banging on about it, but it's great stuff!

Of course - if you still want one, you can have mine for £10 (used once - sort of)

Tried one once
Binned it

I think were all in an agreement here

As above, but tried twice before binning it!

if your doing very thick slate you can use the gun to do a wet clean prefill,let this set for 24hrs,then when you grout to a finish this grout will firm up and you can get a nice flush finish,if you grout in one hit on a 15 to 20mm thick slate it will take forever to firm up and you dont get the same finish imo.
other than that the gun is useless.