It's hard to compare lease terms, especially including tax since tax rates vary among states.
In my opinion ALL of the i3 leases are good deals. It's even more of a benefit when you compare the cost of the initial i3 lease terms. I quoted a lease in late spring for the i3. At that time it was over $700/month with $3000 down. The reason was the very low residual values. Today that lease is almost half the original cost - largely because of more aggressive residuals.
Another way to look at the i3 lease is to compare the list price of a 335i lease to the terms of your i3 ReX. The 335i starts at $43K or so, far below the price of the i3 ReX you've mentioned. The lease on the 335i starts at $479/mo for 39 months with $3K down. That's from BMW's nationwide lease offer page.
Your i3 ReX lists for $10K more than a 335i, and I'll even discount the car by the full $7,500 federal tax credit and bring it down to a price that is still somewhat higher than the 335i. Comparing the two offers the i3 lease is for a shorter term - typically more favorable for the lessee - has a lower down down payment, and most importantly allows you to walk away at the end of the lease without any resale risk.
In the EV marketplace with rapid technology changes and new models on the horizon the ability to walk away is more important than on the 335i which is a car with a long resale history.
So the i3 lease is less expensive than other BMW lease terms, has a shorter term, removes the resale risk and allows you to drive the newest technology BMW has to offer. What's not to like?
Whether a specific lease is $30/$40 a month less expensive from one dealer to the next isn't as important, at least to me. The overriding lease value and walk away option makes leasing a no brainer to me - regardless of the final terms.
Vehicle For Sale 2019 BMW i3, 28,300 miles, new tires