I could never afford root trainers - I use Jiffy 7's for everything - you can buy them in three different sizes from Kays Horticultural (fab catalogue) in lots of 500 (about £20) up to 2000. The largest ones are good for just about everything(45mm) but I generally use mostly the 30mm size.
Definately the best way to sow seeds I have evr found, Often, if they are drying out too much, then I out 5 jiffys with seedlings in a larger pot, say 5inch - when it comes to planting out, the jiffy's separate well and root disturbance is minimal.
good luck, cheers, suzy