There are many Vietnam visa agencies. Everything, including dispatch of the visa approval letter, is online, so their location doesn’t matter.
Let me warn you from vietnamvisaonline {dot} net. First, they refused to ask their bank for some crucial information on wire-transfer. That cost me a full-day trip to their office. Then, the Visa Dept. issued a faulty approval letter; everybody may make a mistake. Vietnamvisaonline {dot} net again refused to ask for quick correction. That cost me 1.5-month loss in visa-validity. When, weeks later, they asked, the Visa Dept. acknowledged its mistake and offered what was then possible; that was no solution to me.