Yup, just try and find a bench vice so you can gently grip the feedneck and hold it nice and steady and you're good. Try and find the right blade for the job- not sure what's best for plastic but they do a selection, or just drop £10 on one of these
http://www.machinemart.co.uk/shop/product/details/cht242-heavy-duty-tube-cutter
and do everyone else as well
As for the Halo and similar designs the feedneck is two layers, with the shell on the outside and the raceway down the middle, so for best results with a pipe cutter cut the shell, then mark the raceway and strip the hopper to cut it separately. If you try and do it all in one go you might make a mess of the hopper as the pipe cutter won't run as well once you're through the outside and it's trying to cut whilst only bearing on half the shell portion of the feedneck.