Half-salt is probably safer, since with pure KCl it's easy to overdo it and have problems. It's the ratio of Na to K that's important.
It's also unfortunate that Potassium salts have a bit of a metallic taste that puts some people off. Using them in moderation tends to help while still reducing sodium content.
Also, epidemiologically it's important to remember that sodium content is often correlated with highly processed foods, cured meats, etc. so determining the effect on sodium in isolation is more tricky. I don't think you see the same strong links with something like Miso consumption, or the smaller amounts of table salt used on vegetables.
It's important to have salt ON the food in a place and form where you can taste it, rather than bound up in a bunch of preservatives where you're getting the sodium without the strong salty taste to limit your consumption to something reasonable.
