Question is - how cost effective is it?

From the Kemco Oil web site...
Octane Supreme 130
Octane boost-fuel additive that really works. 2-16 point increase on octane. Turn a 93 Octane fuel into 101 with 8 ounces per gallon. CONTAINS LEAD! Fouls O2 sensors and plugs cats. Off road use only

One qt by the case costs $10.42 and 1 qt treats 4 gals. So1.....10.42 + 4 gals of the average 93 octane (roughly 2.75 x 4 gals - yours may be more per gallon) = $21.41 for 4 gals /4 = 5.10 per gal for 101 octane fuel. Can you buy 101 locally for that?