anyone use a hood anchor for canoe on top of car

It looks to me to be a product designed to go under the hood, or inside a rear hatch, creating a place to tie to. I personally run my line all the way down the hood to under the car, where I find a metal opening in the frame to place a hook and tie to that. On the rear, I tie to a trailer hitch I installed for my bike rack. Plenty of after market hitches are sold for most models. They might be only 1.25" hitches, but that is enough for a bike carrier or to tie down boats on top.

That kind gets pinned under the hood. I prefer more traditional anchors, but sometimes your car just doesn't provide good anchor points.

Exactly. My Subaru doesn't have good points to tie the front and back tie outs to, so these work nicely with my kayak.

The advantage I can see with that is it’s positioning is variable, unlike tying to a retrieval point down under the front bumper where the line threatens to constantly wear on the same places every time it’s used. Grind through the paint and there’s a corrosion vulnerability.

For infrequent and short-haul use, I have simply made loops of tie-down rope, and tied the loops through a metal brace on each side inside the hood. I trust my knots, and I inspect them for wear every single time I pull the loops up and out under the hood. Then again, I am taking my kayak 5 miles over slow roads to a local lake. If The trip was highway driving for hundreds of miles, I would probably want the webbing as stronger and less likely to rub up the finish on my hood.

The main strength of your tie-down should come from the straps across your hull over the central part of your canoe. Front and rear end tie-downs, if pulled too tight, have the potential to severely damage your boat. The end tie-downs do serve to help keep the boat from sliding sideways, or sliding forward if you slam on the brakes. You probably already know this, but I didn’t want to assume that and have you accidentally oilcan your boat!