My bulk order of super magnets arrived from HongKong (under 2 weeks) and with help from the guys in our Monday Night Train Group we installed 20 super magnet uncouplers in one night - they worked great! In most locations we used two rows of four 8mm x 3mm magnets. In a few difficult to view areas we used two rows five for a larger uncoupling zone.
To complete the railroad I ordered 200 additional super magnets on line at a price of $9.37/100 (free shipping). That brings the cost per uncoupler down to around $.75. If you order them on line go for the N50 vice the N35 strength ones. The added strength lets you mount them lower below the rail head which in turn facilitates hiding them under ballast.
I want to again recognize Dan Dawdy and his O Scale Resource on line magazine for sharing with us how he used super magnets - mounting them on drywall screws was a very cleaver idea.