I'm debating doing that myself. Wanting to hedge my bets, I went with an annual subscription at the end of March last year, as the 30 day free trial was about to expire on my newly purchased 4 tuner Tablo. We did go through a rough patch last year with some issues, but after the Tablo update to 2.2.8, and with the latest Roku update, Tablo has been remarkably well behaved, and it's more like the "don't have to think about it" appliance that I hoped it would be when I bought it.
I still have a couple of weeks to decide whether to renew the annual or go with a lifetime subscription, and right now I'm on the fence. Several things are running through my mind:
1) Will Nuvyyo still be around as a company in 2+ years?
(It's a private company and no way to know who well they're doing)
2) Will new broadcast standards render my Tablo obsolete?
(I bought a Tivo years ago when TV broadcasts were in analog and 480i)
3) Will someone come out with a better DVR?
4) Will Tablo continue to be stable and dependable?
Unfortunately, Nuvyyo doesn't credit previously paid annual/monthly subscriptions towards a lifetime subscription. That would make the decision easier, but I can understand why they wouldn't want to do that. Anyway, I still have a couple of weeks to decide, and am leaning towards the lifetime subscription, but haven't yet made a final decision.