We used a small one years ago. It had to be wheeled over to the sink and hooked up that way. It worked fine. Would a portable machine be large enough for your load of towels, vigorous enough for felting?

I'm sure it would be large enough for the towels - I'm only talking about dish towels. Whether or not the wash action will be vigorous enough for felting is another issue entirely which is why I'm asking if anyone has experience with the machines. In your experience, how vigorous is the wash?

I have one, one made about 8 years ago, about 16" square footprint. Top load with no agitator post, rather a rotating plate at the bottom similar to many new full-size top-load machines. Spins for a few seconds, reverses direction, then spins againIt cleans reasonably well, though is harsher on clothes than a front-loader or likely a larger high-efficiency top-load machine. It tangles clothes easily, particularly long-sleeve shirts; a load of a few towels tangles less. Has spin balancing problems if you wash one heavy towel with other lightweight clothes. Small tub + average spin speeds = less water extracted from clothes than better full-size washers, and more time & energy use in dryer. Mine has only a single water intake designed for a temporary sink attachment, so your faucet controls water temperature. If you want to wash using hotter water (which you definitely will in cold winters), you turn the faucet toward warm or hot water, wait a few minutes for the tub to fill for the main wash cycle, then set the faucet for cooler water if you don't want to run up your electric or gas bills needlessly.

Overall, the little Haier does the job if that's all the space you have. I'd steer clear of the portable washers with agitator posts - I had one years ago (Whirlpool) and there simply isn't enough room around it for larger/heavier items like jeans or big towels to circulate well, and the twisting agitator rips them to shreds. Keep in mind I haven't used the new ones though.