You can use a bushing wrench on FLGR or non-FLGR. It makes no difference. A bushing wrench makes it easier to remove the bushing with a FLGR, because the plug doesn't have the checkered end. A FLGR plug is open (to allow the GR to travel thru it), therefore, the plug is a little harder on the thumb because of its edges.
Shane is correct. I use my $3.00 plastic Wilson wrench all the time just because I bought it thinking I need it on my box stock Colt Government XSE and Office XS. I guess on a match grade fitted bushing that is tight in the slide a wrench might be of some useful help to have.
Just like Shane said the FLGR plug is a little tough on the thumb but just for a second or two and really don't constitute the use of a wrench.
To answer your question, No you don't need a wrench, but for $3.00 if you use it once it's not a bad investment to have.