A friend of mine has the need measure and cut, consistently, small
sections of small tubing.
I highly recommend the Bergeon "Hand Held Sawing Jig" aka tubing
cutter. It's far from the cheapest one around but it is a real
pleasure to own and use. I usually unscrew the handle and clamp the
business end in my (copper-jawed) mini-vise. Once you're set up and
"in the groove" you can produce clean and consistent tube cuttings at
quite an impressive rate. It's great for cutting any kind of stock
that comes in rods, regular or irregular in cross-section, up to
about 5mm across.
You can see it at the Otto Frei website (see link below) though
they're only one of many suppliers. Rio Grande has it as well (2004
catalog, p. 258, item B).