The advantage of visa on arrival is that you will save your time, money and do not need to send your passport out.
With our Vietnam visa online application, you can stay minimum 30 days and maximum 170 days to visit and get your amazing holiday in Vietnam. You can apply a multi entry visa if you exit Vietnam and want to come back. Normally you can apply visa at embassy but you will have to queue for a long time and prepare paperwork for a visa and moreover it is more expensive than you do online. After entering Vietnam, you can extend your visa if you want to stay for a long time but it maximum up to only 6 months.
Source: https://www.hotels-in-vietnam.com/vietnam/vietnam-visa.html