With a radome (spinning thingie inside a plastic "cake cover"), sail snagging shouldn't be an issue (just add wear patches to the head sails). With an open scanner (spinning thingie without a cover), a pair of stainless rings, above and below the antenna, should keep the sails out of the way. However, I'm not 100% sold on that point and less so on the rings keeping lines out of the way. In short, "radome good, open scanner bad".
The scanner sits on a strut (made from cast aluminum pieces powder-coated - built by PYI, the same folks who do other boat toys including dripless stuffing boxes) secured to the mast by 14 screws. It's not going anywhere in any conditions I hope to see.
The cable is about 1/2" thick and passes through a 1" hole in the mast at the butt and and near the scanner. The latter is sealed with a grommet/gasket supplied by PYI and back up with a lot of Life Caulk. As we replaced an existing installation with another, running a snake for the new cable was part of lowering the old cable (hint: using 3/8" or 1//4" line is a good thing). Otherwise, invest in an electrician's snake lowered from the hole near the scanner's new home. It'll go straight down and can be fished out of the hole near the mast butt (long forceps, bent coat hanger, etc.).
At least Raymarine "allows" cutting the cable and joining the ends with terminal strips. Needless to say, use good crimped terminals on the wires, particularly the shield and core for the video data. Thus, it's possible to have a mast mounted antenna and still be able to pull the stick without major trauma (cutting or pulling the radar cable just to let the mast loose from the boat).
One encounter with a radar beam isn't likely to do much harm. It's the repeated doses, particularly with people on the boat often, that raise the risk level. Also, remember there's "splatter" from the transmitted signal hitting rigging, and particularly the mast, that need to be considered, too. A low scanner, mounted on the mast or backstay, is just not a healthy idea.
We are all just a battery failure away from the age of sail.