How awesome is that little contraption! I want one just to have one! And also it would be great for things I wear a lot like PJ bottoms that don't fill up a load and maybe even for superwash hand knit socks!
And it's funny since you mention it for felting, I recall on an episode of Knitty Gritty, Michael del Vecchio was demonstrating a felted bag pattern from his book and recommended a large rubbermaid container and a plunger for small items and/or people that don't have a washer. I'm sure it would be fantastic for felting most things, but I'm afraid this particular item (I am deliberately not saying because it's for a gift and you never know where the recipient might be lurking (fellow knitter)) really requires a full-on very sturdy and fairly consistent felting for multiple reasons and I remember years back there were several KH'ers who tried non-washer felting options that weren't successful. It might work, though, who knows!
My water is pretty darn hot, hot enough that I feel scalded when I was digging in the washer for them, although I will say that I am fairly sensitive to hot water as a general rule. I even would let the washer fill for a few seconds until the water got full-on hot, drain the cool water out, and re-start with the full-on hot. I did try the dryer thing, although I was trying to avoid it (I've read that it can sometimes cause irreversible creases and such in felted items,) and I actually think I did get it down to size (maybe even too small now lol) but even so, it's still not felted properly and there's a particular aspect of such that will make it undesirable for the recipient (again, cryptic on purpose, I apologize. If you remind me next week I'll explain LOL)
I did contact Brown Sheep just to see if they had anything to offer, but nothing yet. I'm really sort of sad about it, not only because of the gift pinch it's put me in (I was able to get some wool at JoAnn's thankfully) it was my first time using the yarn and I LOVED it and absolutely adore the color range and price, so I hoped I'd found a new staple felting yarn (and maybe non-felted too where I wouldn't mind a single, I find it quite soft, although some might not )