I only have a small flock and not plan to give my chickens to anybody else, so I don't worry about the Marek becoming a hot strain. It's quite expensive for you to vaccinate all your chicks though. I wonder if there is a way you can seperate the powder, so you can use just a small amount each time. I may not want new chicks next year, since my chickens are still young.I am looking into vaccinating next year. I HATE needles, but a friend has a "gun" to vaccinate chicks, similar to what hatcheries use. Looks like a good project for next year.
For a rather scary analysis if the vaccines, read this: https://www.pbs.org/newshour/science/tthis-chicken-vaccine-makes-virus-dangerous