Question about the Skitarii Rangers and Vanguard packs

Hello, I’ve recently been getting into the hobby and I was planning on building an ad mech army. I was hoping to buy one of the cheaper packs of units, and on the Games Workshop site, there are two 50$ dollar unit packs for ad mech, with those two packs being the and the .

My question is, what is the difference between them? The description for both reads,

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This multi-part plastic kit contains everything needed to make either ten Skitarii Rangers or ten Skitarii Vanguard. Included in the box are 124 components – twenty-three heads, eleven of which are Skitarii Rangers, twenty-five weapons, a small transfer sheet one Citadel 60×35.5mm Oval Base and ten Citadel 25mm Round Bases.

So is it the same models but it’s just the heads that make the difference between units? Or is there another piece that distinguishes the two? And if there isn’t, why are there two products that are practically the same thing?

Question about the Skitarii Rangers and Vanguard packs