I'd be interested to see which method works better. I've done the Howard P/Joe Polish 100 sq ft/free room thing with a few companies I've worked with. I can say it worked for some, and not others, and IMO it had to do everything with their execution. I know it says no obligation, but you really have to do a bit of selling in order to make it work. Your attitude and set up to actually make money from the offer is what will make or break it.
I've learned people don't want to be inconvenienced, and for the most part people don't want to be inconvenient either. When you go out to perform the offer many don't know that you have time to do other work. So as you're setting up simply saying you have time to perform other work is a must. After the offer is performed you have to be ready to render more services. Don't go into it assuming you're going to get screwed and not get more work out of the deal. Your mental state plays a huge role in your physical body language, and people can see it and feel it more than you do. For owner operators its easier to have a better attitude because you depend solely on the income. But having employee(s) its very important to drill into this their heads. I've been in that position, and admittedly have noticed how my attitude has affected this specific scenario in making it work or not. Being consistent in presenting the offer from the first phone call through actually rendering work is very important, otherwise you really don't know if its working or not. That way you can properly track your results and make decisions to create a different offer based on your market, or to ramp up the offer if it is working.