Frankly a roi in btc means nothing
It makes a difference to mining because you can always just hold the BTC and wait for them to go up.
Case in point this group buy currently costs around 0.2 BTC per share. If you just hold onto those 0.2 BTC you might do very well if the price of BTC goes up. Assuming the price does go up, to do better by sending it off to buy hardware you need to somehow eventually end up with more than 0.2 BTC at some point in the future.
yes you can do that.. and you are leaving out the value of the gear. the gear has resale value.
So 1 share at 130usd at 600 usd btc is .217 btc.
pay that. and in 1 year 1 btc = 1200 so you have 260 usd / .217 btc
buy a share for .217 btc and in 1 year earn .200 btc then sell the gear for .1 btc you have .3btc at 1200 = 360
the problem with thinking in btc roi is you use 1 path to profit and leave out hundreds of other paths.
This is not to say that buying 10 btc from coinbase today at 6k stashing it in a safe wallet for 2 years completely ignoring it is a bad move. It is a simple 1 way 1 method choice to making money in the world of btc.
Buying a share here is more complex. Doing both is more complex. doing that plus selling some gear on ebay and mining in your home along with setting gear up for local friend if far more complex. This is my limit. Others do all of that and write programs for mining and others do all that and write programs for new coins.