"folk instrumentation" makes them sound like early Ulver or Empyrium. Finntroll are full on 'humpa pumpa where's my jumpa' metal with the polka dancing and organ grinding. I'm sure they even have a monkey in their ranks somewhere holding out a hat for loose change handouts from passers by.
If you don't like Finntroll, you will hate them. There is no middle ground here.
I think Finntroll fits the circus metal tag better than anyone else, and the organ grinder images are hilarious...and I'd get both of the Armageddon albums if you can find them cheaply enough...