I was on this service for some time as a tester. Because I'm a dabbling minimalist and frugal enthusiast, I got my cellular data down below 250MB per month. As far as I can tell, there isn't a plan out there that can beat $22.50 per month.
Imo the big downfall is the requirement to use a Nexus 6. It's not a bad phone, but it also isn't terribly good. I recently went back to iPhone and joined another slightly higher but still low-cost carrier.
Do you mind sharing which carrier you have now? I've been looking at switching to one of the lower cost carriers, but haven't seen one that supports the iPhone.
Cricket and Ting both support iPhone. If you have an iPhone below 6, you need Ting if it's a T-Mobile iPhone and Cricket if it's an AT&T. I think you can use Ting with the CDMA iPhones. I'm on cricket personally.
Imo the big downfall is the requirement to use a Nexus 6. It's not a bad phone, but it also isn't terribly good. I recently went back to iPhone and joined another slightly higher but still low-cost carrier.