They are pretty cheap, I wonder if it makes sense to put a few of them online?
If a TVS fails, it can fail shorted or open. If it fails shorted, you will know it right away if you have a good breaker! If it fails open, you will not know about it, and you will have no protection. So having several do make sense, because if one fails open, the others are still protecting.
If you are installing them in an engine, then I would recommend two in each engine for the same reason. You will have a backup TVS in case one fails, with the added bonus that your protection travels with you if you take any of your engines to a friend's house for a play date! Also, I like the idea of protection right on each engine because that puts the protection as close as possible to the place where it's needed, in this case the sensitive and expensive boards in your engine. I can't prove that there's an electrical benefit to installing them in an engine vs, at the transformer, cuz like Rob said, they are "electrically equivalent", but my gut tells me that it's better.