For those who really can not decide - maybe as per picture below - Little Skeeters - are sleeves that slide into 20 gauge chambers to use 28 gauge shells. Obviously firing 28 gauge in a 20 gauge - so no weight savings, etc. I had bought an MEC loading thing for 28 gauge - do not have one for 20 gauge. I have an O/U in 28, then a SxS and O/U 20 gauge. The idea was that I could use my reloads in the 20 gauges - have never used the Little Skeeters yet - still have 20 gauge shells...
my experience is very limited to tried once and great of you want to hit a barn
Cheers