I've used both the Qlink and Harmonic Protector. I've been using Qlink for several years and have been impressed with how much more energy and endurance I get with it. I recently lost the Qlink (string must have broken) and decided to try the Harmonic Protector after reading about it on CZ and elsewhere.
I've had the HP for close to a month, and it just feels like too much. The congestion around the heart you mention is definitely there, and I can never wear it for 24 hours straight. Also it seems to passify me too much while wearing it to where I think it decreases creative thinking and emotional engagement.
I've just ordered another Qlink and am expecting it today. I'll keep trying the HP for awhile, but I'm guessing it won't be long before I'll be back to the Qlink full time. That said I also feel the need to remove the Qlink when I have to be at my sharpest and creative best - but for all other times, it makes me feel calmer, more patient and more energetic.