Its just an hour flight. Why not. The service are quite good as well and some do offer drinks for free. As its domestics, check in is really quick and you can even arrive in the airport 30mins before departure.

Yes as you dont need to go through immigration. You can do the check in on your phone, drop your bags and then walk to the security. I have done a lot of one day trip previously and I can really plan my time as the trains are pretty much on time. Also most flight are flying off Haneda instead of Narita. I think now there are some domestic flight from Narita too but not many.

why budget airline? The cost is a lot cheaper than Shinkansen?

Given the same choice, think I'd go with shinkansen unless you land in Narita and you're flying almost immediately to Osaka. Otherwise the time and amount spent travelling to airport, the flight, plus landing and getting your stuffs etc is easily about the same as shinkansen (or even more).

Actually if you fly from Haneda there is only one check point which is the security check point. It just like taking a shinkansen. But then if I were to go to Osaka from Tokyo, for business I will just take the shinkansen. However if its further south like Hiroshima of Fukuoka I will take flight. Tried once to Fukuoka and it was damn tiring for 5-6 hours....flight just 1 hour.

I see. I find flight troublesome you know, with boarding and all. Shinkansen is faster and hassle free. Given a choice with all conditions the same, I'd still choose shinkansen for the comfort (more spacious than planes!) if the train ride is 2-3 hours. But yes if train ride is 5-6 hours vs flight 1 hour, the latter is definitely better. Unless you wanna enjoy the scenery hahaha.

This site is selling: https://shinkansen-ticket.com/?gclid=CjwKCA...axoCdH0QAvD_BwE

Any idea whether they're an authorized agent or simply an independent agency?

Can still reserve though? Not sure how the payment goes as it's not elaborated.
https://www.jreast.co.jp/e/ticket/reservation.html

not sure if peak time or promo time to buy tix for early april

its 1600+ with ANA cheapest now from google flights