... if you issue parted /dev/sdx and then print, you are able to
see all the partitions on sdx, including flags, filesystems a.s.o.
Hadn't tried that, but it doesn't look like any more information than I
can get from fdisk. E.g. parted's 'print' shows the partition type, but
doesn't actually test whether there's a formatted file system there
unless you're doing a file system operation on it. And it feels safer to
me to just try and mount a partition temporarily, and read-only if you
really want to be careful.