I started using them this past year and I love them. I have not had any problems with them. At first I did worry a little about the strength of them, but they look to be the same thickness and steel as the hooks I use, so why wouldn't they hold up? I even hooked and landed a 6-7 lb Steelhead using one and it held up fine. The pros are the obvious, I can change out a fly quickly. Also the open ring does allow the fly to have a more natural "loose" action on the end of the line. I use them spin fishing as well. The con's would be it is an extra piece of hardware that a shy fish can see and get turned off of the offering. They are tiny, so you may need a pair of hemos to put on/remove the fly, especially with the smaller sizes. Also I like to break down my rigs at the end of the day and when I reel the line in with the fast snap on it does catch on the wire guides. I think the brand I use are Mustad, but I'm not sure as the small fly shop I get them from repackaged them into packs of six for .99.
Tom.