The interface is anything that sends SMS (well or a google spreadsheet, which can be viewed on many devices), and all party members can get an alert on spending.

I like it

Affirmative. The text input is as low friction as possible, and a spreadsheet is as flexible as possible.

We also couldn't figure out the YNAB methodology. I know people swear by it, and we probably just didn't put in enough effort. But we attended a webinar, made it one month, then couldn't figure out how to duplicate our budget for month two. It was just different than how we are used to thinking about finances.

Also -- and this is probably the biggest thing -- I built it myself. For 99.999% of the population, YNAB is an objectively better product. But as a developer, I can't overstate the satisfaction that comes from my wife using something that I built multiple times a day.