Nothing is free. UPI isn't either. Whether it is paid for with a surcharge, implemented in the product price, or funded by your taxes it is being paid for by someone.
It is not anywhere close to being pervasive, at least not so far.
Of course not, it's official rollout hasn't happened yet. The timeline is next year. But in the place where it came from it is universally accepted, and country wide adoption is rolling out in several countries right now (it requires bank level support, so the moment your bank has it then it's possible to use). And payment processors all over the EU support it. Heck I just used it to buy something from Aliexpress.
Wero is more akin to the Zelle system in the U.S.
It's nothing like Zelle. Zelle is a person to person transfer system. Wero is a person to business system first and foremost. The thing is with Wero is that once it is implemented then a personal Zelle like system becomes as easy as having an app generate the appropriate QR codes. Most bank apps already let you do this. And some payment terminals are already starting down this path (e.g. if you're ever in Amsterdam and feed a can into a can deposit return machine it'll spit out a QR code which if you scan proceeds to close the transaction via Wero to refund you your 15c.)
Having used UPI (I regularly travel to Pune) as an end user there's no practical difference (except for the offline capability I didn't know about until just now) beyond the fact that it hasn't been adopted at a payment terminal level. But that's coming. Very few Wero transactions charge additional fees.
By the way there's renewed push back against UPI in India right now. The benefit of a government system is that it is centrally managed. The downside is that the taxman starts knocking on your door for small individual transactions. I'm not a believer in that pushback, I'm just saying that there's plenty of people the idea of the government directly looking into your transactions tickles some the wrong way.