In my opinion, investing money that isn't mine into something too speculative is a huge no-no. Why not just use your own money instead? That way, you don't receive any crap if ever the investment goes bad. They already aren't convinced in the first place, so why force them?
This would be the key point I think.
Putting it aside, I don't know why the OP brings land into the equation, unless it is so cheap that you can buy chunks of land for $50. The normal is that you will have to save several months at least until you can buy something, whereas gold and bitcoin you can buy small amounts. The downside of gold is the premium he will pay both buying and selling and if he does DCA bitcoin he should think about buying a HW.