Hi Terry,
So, i have used them in the past a little bit.....
My thoughts:
They are more fidley than a fly to tie on ( as you have the whole fly to grip when tying the knot - you only have a wee clip to try and hold when tying it on)
They can be tough to thread the fly onto the clip and they can be tough to get the fly out of also...
They fly with 'move better' as the hook eye can 'swing' within the clip
The advantage of the clip is that your droppers stay the same length no matter how often you change fly
Maybe give a packet a go, but to be honest i think they will more hinder you than help you....
I did once hook and land a trout 'on the clip' instead of on the hook
regards
James