Chances are probably only 50/50 that the gunk kit will do the job. The nail I picked up earlier this year was on the shoulder and the gunk kit would not have fixed it so the car would have had to be recovered with all the hassle that entails.
Incidentally, unless you have a full size spare then you shouldn't fit it on the front as shown in the vid. Also, if you do use the gunk then I think you have to drive the car immediately afterwards to spread it around in the tyre and then possibly top up the pressure again.
Space savers are not a patch on a full size spare either but better than the gunk. When I carried a full size spare in my old TS2 the indications were that it might have taken about 0.5 mpg off the fuel consumption, that's all.
I believe that the recovery people (AA/RAC etc.) now carry generic spacesavers with wheel hub adapters. These allow you to drive to a tyre place and they collect them later.