I've tried most and i must be honest some are better than others. The trouble is different dropper for different situations and amount/type of bait being fed etc etc. I now make my own, cheaper (coz they do get lost) and better. better because you can design for the intended situation/bait.
I've got a Fox one(medium) and it works fine. I also have a selection of the round brass ones in various sizes. The smaller ones are great for low bait quantity and low splash entry.
I use both the Fox and the Seymo bait droppers in small and medium sizes.
I prefer the Seymo, maybe because it has been used a lot more, but the small ones are really good, very little entry splash and I've never had one go 'wrong' on me.
Yeah if I had to buy one it would be Seymo.
Speci, next time you are over I'll bring one with me and you can have a go. In certain circumstances they are a must, depends on flow, depth and what you are trying to feed.
I got some on ebay last season. There are a few different sizes, I got some which were advertised as medium, which were about 10cm diameter. They are black and made by a company called Northern Angling I think.
Cheap as chips (£3 for a pack of 4) but well made.