I have more or less given up on merino for bike use but still use it for walking . So, I was in M&S today and noticed they had lightweight l/s merino jumpers for £35 which is cheaper than a lot of fancy merino base layers. Would they be of any use as a base layer for outdoor stuff or are there other ‘issues’ that would make them a waste of money?

Gap ones work well. Not very different from an icebreaker. Knit is a bit more open so not as warm maybe and slightly more prone to snagging.

I’ve bought thin merino jumpers for £15-20 from TKmaxx before as winter bike layers, they’re fine. V-necks are good as they make space for a zip-front top and jacket plus a buff. Or you can get a classy polo neck for a proper deep winter base layer.