I've done both. Flat towing isn't safe, period. I'm floored by the suggestion that it is. You haven't friggin done it if you think it's safe.
I bought my B2 a long time ago, I forget when, in Virginia Beach. I had a '91 Ranger, swb 4x4. 4.0 and 5-speed. I took a towbar with me. AFter I bolted the B2 to the towbar it started to rain. I was going about 3mph to keep from sliding. Then, I went through the first intersection and suddenly traffic in from of me stopped. The B2 didn't get the word and it jackknifed me in the center of the intersection. I waited embarrassed for the light. Then I was on my way up the onramp and traffic again stopped. And I jacknifed again. Then I was on the interstat and had no other issues.
Here's the main problem flat towing--the steering box doesn't like to be forced the wrong way. The tires have a 15-1 advantage against them and they aren't interested in turning when you are.
But I'm sure it's absolutely safe besides all of the hazards I've pointed out.