First you'll need to pick a fuse/polyswitch that shuts off at ~half your target current draw. Eg if you want your protection circuit to kick in at 5A draw and you have a polyswitch/fuse in parallel then some ratio (directly proportional to the resistance of the polyswitch and fuse) of current will flow through the fuse and some through the polyswitch. Obviously if they have equal resistances then if 2.5A flows through each device you'll have a total draw of 5A.
the "indicator fuse" has a much lower reststance than the polyswitch - no exact match is made and - yes there is a slight possibility you get a missing indication.

So what's the point of your polyswitch again? Now the whole thing will stop working and you'll get the call "it doesn't work." Ok, open it up and you'll see the "indicator" of a blown fuse. But you'd have seen that anyway if you had just used a fuse in the first place without the polyswitch.... So what does the parallel polyswitch do for you?
the 'thing' will recover from accidental/intermittent shorts which It would not if only a fuse.

ALso, in VERY few cases we have, for purposes of investigation, remeoved one of them

Erik