Can't comment on the summer version or the 151s, came across both of them while browsing but my wife had already bought me the knox base layers. I don't feel the need to get anything else for summer. The original ones i have are on sale now as they've released a new pair. Also @Android853sp is right about the collar, it isn't as tall as the heatrub version but way more so than my knox.
I’ve bought a few of these over the years, great quality. You can normally find them in Blacks for about £70.00. https://eu.icebreaker.com/en-gb/pro...-long-sleeve-half-zip-thermal-top-ibb04367013
