Just seen the Hasslefree postings re the dragon decals on Facebook, but not being a Facebooker, decided to post here instead.
I'd quite like variety in both size and style of the dragon decals, mostly because I'd prefer to use them for individual figures, rather than necessarily a group/clan/gang. Without knowing what sort of shapes are involved, it's a bit difficult to suggest sizes specifically - e.g. a long thin dragon would go well on an arm, leg, chest or back, but for a round or heater shield you'd be better off with a "squarer" dragon, like the red dragon on the Welsh flag, say, and that might work well on the back of a figure too. I'm thinking both tattoos here and emblems on clothing/armour.
I'd likely be using them for 25mm/28mm figures predominantly, but again not knowing what they're like, wouldn't want to rule out the possibility of larger decals, for flags or even wall-paintings, for instance, especially if some are in bright, contrasting colours. Even straight black or white "outline" dragons would look impressive on a suitable background, of course.