As a recent convert to a new tubless bike (and upgrading my old bike, 2010 specialized, to lend to a friend), here is my take:
1. Is it worth it? As with most things it depends. If you ride any of the following, it’s probably worth it (outside these areas, maybe it is too – but I don’t know them enough to say): soft/loose areas or desert regions full of things that will cause small holes (goatheads, cactus, etc). The short is that lower pressures give better grip as your tire has more surface area (no surprise here) and the holes of any small punctures are filled with the sealant – keeping you from needing to manage much with your tires. There is the physics of rolling resistance removed without the mass of a tube as well, as others comment.
Of course, you generally still carry a spare tube in the cases you get a bigger impact (“snake bikes”, etc).
My experience: To date, there have been no times in which I would get my bike out for a new ride where one, or both, tires were toast. Also, riding through areas I knew were prone to goat heads/cactus I didn’t see any issues that were not handled by the sealant filling the hole (I am in CO – so more desert/arid terrain).
2. Which sealant? I’ve run Stan’s and Orange Seal – so far I prefer the orange seal. First they include the stem adapter – so no need to finagle anything. Secondly, and entirely subjectively, I’ve noticed faster seals – even on the bigger segments (e.g. sealing new wheels where the rim tape allowed more than it probably should have…). However recently there has been a buzz about the newest finishline release…
3. Added maintenance? You pretty much just need to re-seal every ~6mo. If you notice tires are not holding quite as well as before – it may be time. Also if they sit for a while (6mo+) you may get the sealant pooling and hardening (aka “Stanimals” for stan’s :)). Finally seating a tire takes some more work (you will need either a charger pump or an air compressor) – new tires that are held in a non-round shape may need a tube in them for 5-10 minutes first to get them seated in a wheel, then pulled out to do the tubeless way.