I may should say this topic can be set as solved under the condition that it works for me.
It is about a usb-stick with an iso-image on it, Made on a linux machine putting a linux-distro on in, bootable device, to test the distro. I did not like it, disarded it, went back to gparted, formatting it as msdos fat32. This worked well, linux tells me, full space available.
The point is, this device goes from a linux to a BSD and rarely to a Windows machine. That is why I needed the msdos fat32 format. While linux says that everything is okay, BSD mumbles correctly, that there still is a boot partition on the drive.

Once again it works for me this way, not claiming the solution for encrypted partitions or slicing and dicing. So this is a particular solution, but probably helpful for others, who are not using encrypted slices or something just made for ufs. Although there is a slice1.

Code:

# clean the whole partition
gpart destroy -F da0

# set a mbr on the same
gpart create -s mbr da0

# fill the partition
gpart add -t \!12 da0

# format ins msdos style (fat32)
newfs_msdos -F32 /dev/da0s1

Resuming, some things take time. Damn thing.

This would or could work for make it bootable for ufs or BSD, I did not try yet

Code:

# clean it all
gpart destroy -F da0

# set a blank BSD partition 
gpart create -s bsd da0

# set the whole partition for usage of FFS(2)
gpart add -t freebsd-ufs da0

# format it (ffs(2))
newfs -U /dev/da0p1

This is an approach for flash drives

Code:

# Think twice about the name of your device
# clearing the MBR
dd if=/dev/zero of=/dev/da0 bs=2m count=0

# formatting it
newfs /dev/da0

# test test test
mount -t ufs /dev/da0 /mnt

# note da0 may, or may NOT be the correct device - check messages