(my two cents)
...personally....i prefer a reciprocating saw to cut spiral....i've seen guys that use a grinder with cut-off wheel....and it looks really nice...(i couldn't get the hang of it...so i stick with what works for me)
...when you're done cutting your piece...take some time and trim off those barbs left from the diagonal cut seam...not only on your piece...but also on the drop-off...your partner will appreciate it...
...and whoever tells you NOT to cut the seams for your take-offs is 100 percent correct....(the larger the spiral the more important this is)
sawzall works best for me. then i mastic my seams. really nice looking jobs. i kinda miss working with the stuff.
Just did a small spiral job. Reducing trunk line. I used sawzall for the pipe lengths and unibit to start the holes for my registers then snips. I used the curved registers, not the boxes. How can you install the registers without cutting the seams??