For our car, we were using PayTM fastag long back. It was undoubtedly the best. Easy to load, easy to see balance etc.
When they shut down, I started searching for another one and finally decided to take ICICI fastag.
Process was all online - and I got it by post within a week. Here aer the deatils of the fastag
https://www.icicibank.com/personal-banking/cards/prepaid-card/fastag
There was an app for manaing the fastag toll - some e-toll app (
https://etoll-by-icici-bank.updatestar.com/en)
Now it is discontinued and I think they merged it with iMobile app.
This is the web link for managing fastag account:
https://fastaglogin.icicibank.com/CUSTLOGIN/Default.aspx
You can upload RC images, KYC update, fastag image, vehicle image etc.
You can see the transactions, and other notifications etc.
I have felt it to be very comprehensive and detailed.
One difficulty I face is to find out the fastag balance. I usually check it through Amazon Pay while recharging fastag.
I have also linked the fastag to HP Pay app (there was an option to link, but I haven't done anything after that).