Bang on,on of the most useful threads on this site,ive used both of the ones youve posted and also a 16 gear range changer(although you dont really need it un-less your on the drag).Wished youd have posted this a couple of years back,when i was a newbie.I got sent out in 4 over 4 one morning,at silly-oclock and there was no-one in the depo to show me how to use one! i spent 25 minutes stuck in 4th gear,panicking trying to slap it over and all sorts,i was about to turn around and head back to depo and wait for some-one who could show me,when by pure luck i hit the switch and hey presto! sussed it.It was a cold saturday morning and i had to pick-up the keys from the security office,because the traffic office didnt open till 8am.Would have looked a right prat if i hadnt found the switch, 
Maybe you could put a thred for some of the auto-boxes for all us class 1 wanabees sometime 
i definetly wouldnt want to make same mistake in a artic! you cant always ask other drivers,especially if your on the 3.30 saturday morning run!