I've had the same thoughts.
I had purchased and used the bot for 1 month. Initially I used it without mirror mode, but received a 3 day ban.
I then purchased mirror mode and started using the script. Due to mirror mode issues, the script worked about half the time (not Chris's or this scripts fault - I spoke to Chris on several occasions about my issued which he helped me out with, but most of the time they were out of his control).
The requirements associated with this bot, mainly the high level account and gear requirements, makes this a high risk investment.
It requires a lot of time, as you calculated, to make back the initial costs.
If you can somehow bot all that time without receiving a ban, it would be worth it. But I personally don't think it's very realistic.
The only thing you forgot to calculate in your post is the price you put on a pet/collection log uniques and time saved doing it yourself.
You also forgot that you can run more than 1 account at a time. So depending on those factors it may be worth it for you.
For me personally, i'd be much happier buying a lifetime version of this bot, even for a higher price than the current payment structure.
Unfortunately, as it currently stands, the risks and costs associated with this script aren't worth it for me.
But everyone is different, just scroll up and see some insane signatures haha