They definitely drain the life out of you, thus the name. Every time I do them, I'm sucking wind and wanting to find a bench to sit on, but mainly just pace a little bit until I can catch my breath and unload the bar since I won't be doing any more damn squats that day. Ha.
I'm sure everyone is different. Plus, I think you mentioned in the video you posted that it was your first ever Widowmaker set, so I would put away the "Jump-to-Conclusions Mat" and just see how your body adjusts to the demands you're asking of it. You'll probably find that you'll be able to handle the intensity after a few laps around the block.
Also, a word of caution. Keep your Widowmakers to the first 2 or 3 cycles out of 5 only. Don't ride them out for the full 5 cycles. Not a good idea.
I mean, you COULD do that if you wanted, but I would just take the advice. I'm just talking about general programming, not necessarily this Hardgainer template. Not sure if Jim would recommend using this same template for 5 cycles or not.
All of that aside, I love Widowmakers. I've been running my 5 cycles with PR sets + Widowmakers in the first 3 cycles, then just PR sets in the final 2. Working out great.
Whatever you choose to do, good luck!