For PR you need to be on a Non-Immigrant Visa for 3 years paying taxes etc if going the employment rather than family route. You can do that on your current "B". Going to DTV and then back to a Non-Immigrant is going to reset the clock to zero whterh it is B again or LTR.
Good info - looks like the agency is responsible for obtaining the visa and then it is up to you. Fair enough is that is the service you paid for. As for follow up the only real things are your TM30 and TM47 (90 Day report) - just ask in here and people can help. As you know for extension in-country you would have to basically supply all the application info updated along with residence requirements depending on the Immigration Office. Leaving thailand and returning gets you another 180 days without resubmitting documents.
A few of us had suspicions about a flurry of recent posts about them too. :-) Maybe just overzealous marketing? As long as all paperwork supplied and they are an approved DTV Soft Power supplier it should be no issue getting approved.
Vietnam Embassies have asked for proof you are still in country a few times according to lists in this group. Asking for time stamped receipts in country.