We need these TLDs like we need a .holeinthehead
The downside from buying it from Google is if you were trying to maintain anonymity about the ownership of a network of sites from Google itself then those particular TLDs probably won't appeal to you. However, not knowing if all registrars can see the true site owner instead of the private registration, it could all be moot anyway.
While some of the TLDs may be useful the general population isn't ready for it all and quite often still go to .com even when you have a .net. Most people have no clue about the majority of domain names they even visit because they find the site in search or from an ad and click it and maybe bookmark it but rarely ever type it.
I own a couple of TLDs off the beaten path but I certainly wouldn't launch a serious business with it unless it was something really compelling and easy to use like "discount.book"