Been using it exclusively (well, qutebrowser tests aside) for a month or so. I miss nothing from Firefox/Iceweasel. It feels like an old FF, but it gives you all you need without the "fancy stuff" Mozilla added in newer versions. I don't use flash, whatsoever. But I have no need for it.
Regarding the source I've got it directly from their servers instead. Updates are not as frequent as the Mozilla ones. Manual updating is not a mess.