Jennifer, Meco is a nice merino/synthetic blend with cocona blended in (faster drying times). Its a nice compromise between the strengths of merino and synthetic without most of the weaknesses. I like a hoody with thumbloops because I can leave behind gloves a hat and it helps with sun protection when I'm wearing a visor…
…and no, you totally don't need one! But should you ever go looking for an uber-technical base layer, its a good one.
And I made the mistake of putting that blog on my rss feed, so now I'm automatically made aware of future highly desirable unnecessary gear to buy.
Prolite gear has Rab Meco: https://www.prolitegear.com/rab-meco-120-ls-tee.html
Prolite is a small outfit out of bozeman, MT. They have a really nice selection of specialized gear and they have a good presence on this site as well. Check them out.