I like the convince of always having extra spools on hand! Nothing worse than running out of spool thread while working, trying to get finished and have to go to the store to purchase what you need. Although, I was surprised when I ordered the "free spools for life" at the cost of shipping each time I need more.
I have my original 18 volt trimmer, blower and hedge clipper I purchased almost 10 years ago and all work extremely well. I since have purchased 2 more 20 volt units and a 20 volt blower. AWESOME PRODUCT !!!