if you want any problem the other tanks have for problemsin your new tank, and be a problem there also,, go ahead and use them to cycle the new tank.
No, simply moving water over isn't going to cycle the tank, it should move some sort of bacteria over in small quantities, but nothing even close to an "instant cycle". and instant cycle would be moving a filter and established bacteria colony that is sized for the fish, over to a new tank.
Again though, if you have any doubt about your other tanks and them remaining problem free, I do not recommend you start this tank off those cycles. it's just asking for a 3rd problem, on top of the first two. let this one build new and separately, and worst case use it to do a big clean on the others and start their cycles new off this one when it's done if they keep giving you problems. a fresh start, with a tank you did from scratch and hopefully no problems.
You would not have been happy with a 20 long, I have one, the extra 6" of depth on the 29 makes all the difference in the world. the 20L seems so tiny, like a stretched 10g, it's the same footprint of the 29g, just 6 " shorter and 9 gallons less water.
a 40 gallon long, is pretty sweet, but not cheap,, and that's not something you are gonna find just anywhere either. places rarely have those laying around.
it's like my white whale tank, a 15g High. Same footprint as a 10g but 6" deeper. NOBODY has them at any price. I want those for my 10g
tank stand for the top and bottom shelves....... grrr.