Embassy V Agency

I have been advised by a reputable local travel agency that it is necessary to avoid visa agencies and apply for visa directly through the consulate (Vietnamese embassy UK - however I am Irish). I was also advised to apply for the visa ahead of arrival as this option may not be applicable for my nationality. Can you confirm that the embassy is the only option for my nationalities visa application or are visas obtained from agencies such as this valid? P.S. I will be travelling from Laos into Vietnam either by bus or plane! Thank you..