Been using my 40V Ryobi everyday. Dunno how long it's going to hold up but I like it fine. Definitely lasts longer than 15 min.
On a budget I vote 40V Ryobi. Price no object, the Echo looks awesome. Re: the wife, there's a YouTube video where a guy compares the 40V and 18V Ryobi's. He says the 40V battery is much easier to remove due to retention tab design, and he actually wants to replace his mother's 18V w a 40V for this reason as she struggles w the 18V batteries.