Canadian81,
I have had the .25acp breech plug for about a year now and I really like it.
The benefits would be you can load up the brass before going out to the range. I load up about 100 or 200 at a time and you don't have to mess with loading primer carriers while shooting. The biggest benefit would have to be they are almost totally blow-back free, I just get a light soot ring around the back of the brass at the breech block. With the primer carriers, it's all over the place. You can reuse the brass if you would like, just punch out the primers, clean and reprime. I think a brass tumbler would be the way to go, because I haven't found an easy method as of yet. I have washed them, but they turn tarnished and need to be tumbled or something else. Guess I should go ask at the BPCR forum and find out how these guys clean their brass.
I have been loading them and discarding them for the most part, they are still way cheaper than Knights "Full Plastic Jackets" and 209 primers.
I mostly shoot 777 loose powder in FFG & FFFG grades and have not shot pellets with this conversion as of yet. I have also shot some Black Mag'3 powder with no problems. If you are a pellet shooter, I am not sure how it will do.
Just make sure if you order it you order the right one, they come in 5/8" and 7/8" sizes.