I've used Viettel's i-Share service a few times, mostly when my roommate ran out of credit in the middle of the month and hadn't had time to top up. What I noticed most is the 5% transfer fee, which is quite expensive if you transfer a large amount; for example, transferring 100k costs 5k in fees. So I usually only use it in truly urgent situations and not as frequently as bank transfers.
Once I forgot my 8-digit password and had to call the hotline to reset it. It was a bit inconvenient, but not too complicated. Compared to Vinaphone's 2Friends, Viettel's transfer limit is much more flexible, because 2Friends limits it to 50k VND per transaction, so transferring double that amount would require two consecutive attempts.
Back when we were students, we used to use these services at the end of the month. Looking back, I realize how lucky we were to have them to get by temporarily before e-wallets became as popular as they are now.
Does anyone remember which of these three services you used most often in the past, or have people completely switched to e-wallets/banks and hardly anyone uses these methods anymore?