Have a line on both a VN42 Mitremite or a Cassesse C89, about the same prices, both in good condition. Now...I'm used to the Cassesse, and never used the mitremite, am I correct in assuming there are heads that need to be changed every time you need a different size v nail? I know with the Cassesse, it's just a cartridge that slips in easily. And yes...I like easy, but would also like it to last.... Thanks in advance!!