I've tried this twice now. So far, I get very little feedback, but what I get, I find useful. Aleksejs Truhans suggested to me that people could put a blank sticky note on the door to vote for happiness level without leaving a comment. That seems to help. Also, I only have two categories: ! (good) and ? (bad). I'll try this some more and adjust when I need something more. The best feedback I received so far is "I can't read the code on the projector", so I hope for more useful feedback in later engagements.

I'm Canadian, and I've never had problems going into the EU. Of course, I don't say "I'm training", but I do tell them I'm consulting, and it's not a problem. In my places, for example Turkey, they don't speak English and so they don't ask questions.

I have had a Detroit CBP guard tear the I-94 out of my passport before realising that I'm Canadian and that Canadians don't have to surrender their I-94 when they leave the US.

The US CBP and ICE will usually follow that with several questions about the nature of your trip.

You could also hire Canadians to do the work for you, since training is explicitly allowed under NAFTA for Canadians who apply for a TN-1 visa to work in the US. Janet Gregory knows the exact paragraph in the statute to quote. You would simplify your life by hiring an American, but hiring a Canadian -- or, I suppose, a Mexican, although I haven't tried that -- should work almost as well. I don't know how Canadian border patrol treats Europeans teaching in Canada, but I could only guess they'd treat you better than the US CBP/ICE would.

Bas Vodde and I spent a month working with different teams in the same company last year. When we met, we'd brag to each other about how much code we deleted. It's an obvious sign of improvement.