Its enough for me to complete my day to day work.

>Does it allow one to do everything one can do in browser Jira?

I dont think it can do the dashboards and reporting metrics, but for the 'issue' work yes.

> Set custom fields

Yes. Although i had to maintain a map of custom field names to what they actually were, or you'd see cf_023042432 as the name.

> handle multiple boards

I don't use jira this way to know what it means, is that the same as multiple project prefixes (if so yes, i dont know what boards are).