Sunviet Travel (Visa Expert): Too Good to be True?

I can vouch for Sunviet travel and Johnny Le Manh Hung. I visited their office on Tran Hung Dao near PNL, saw 4 busy workers there, and a stack of 25+ passports in process. I have used  Johnny's services twice.  Once for a visa approval letter for airport visa-on-arrival. Then on November 19, I got a 3 month visa extension. I contacted him via email, he sent a nice woman who spoke English to my house to pick up my passport, and 1 week later she returned and I paid $50 on delivery. (An extension is just a stamp with dates in your passport. I assume you are in Saigon with your passport, otherwise would you mail your passport to Sunviet? No travel agents in Phu Quoc? ) He is active on the Facebook group "Vietnam Visa Agents"  where you will find lots of other visa agents. You can search Expat.com for 'extension', I read one guy got a lower price from a travel agent recently.

Hi... wow thanks for the information! Now, I'm in no doubt at all to use their service.
I talked to Johnny via phone and he said it's okay for me to just mail my passport to Ho Chi Minh. Which is a little scary but I guess I have no choice.
Anyways, I'm still thinking about it, either I travel to Saigon for some days to process the visa or exit again or mail him my passport.
Sad but extending, renewing and processing visas here on Phu Quoc is really a fuss. Travel Agency either don't do it or charge you with high prices. My friend who got his visa extended last October caused him 200USD for 3 months. I'd rather buy a ticket to Siem Riep.
Anyways, thank you so much for your help! Means a lot! Xin Cam On!