Product review (4 stars): Excellent for the price in terms of taste and functionality
I bought this after blanching a bit at the $/gallon for some pitcher-style filters and learning about the limited range of substances filtered. I have a stainless restaurant counter and a wall-mount faucet, neither of which lends itself to undercounter filters.

Shipping was quick and the filter was packed will. The vendor was kind enough to use cornstarch packing peanuts, so I didn't have to deal with more unrecyclable packing material -- thanks to them for that! Two threaded adapters, with appropriate rubber washers, were included for a variety of faucets -- the unit happened to fit mine correctly without use of an adapter. The threaded mount spins independently of the plunger/aerator component, so you can tighten/untighten without having to spin the hose and filter around. It's knurled, so I got away with screwing it on finger tight using a rubber band to get more torque rather than using pliers (the knurled grip would also hide tool marks better had I not been able to get it tight enough without resorting to a tool). It's also good practice to use a strip of teflon tape when joining threaded plumbing parts, but the CuZn threaded mount had good tolerances -- no tape needed, and no feeling like it was going to cross-thread as I installed it.

The aerator on the faucet neck mount works nicely.

A narrow hose runs from the faucet to the unit (OK, that's obvious). That means you've got loose hose either dangling from your faucet, or wrapped to keep it trained, zip tied, etc.  I don't think it's reasonable to ask the vendor to include clips to train the hose on the diversity of faucets this can be installed on, and I was totally satisfied with what was included. A buyer may wish to think about how discretely you want your hose run and what kind of clip or tie that will involve.

The filter is activated by pulling a plunger on the faucet neck mount. The plunger is spring-loaded and held in position by water pressure. Mine's fine, but note that if you have poor water pressure at your faucet you may need to keep the plunger pulled with one hand while filling (so, YMMV). This means that turning off the water "deactivates" the filter -- that's fine, too.

I have municipal water that tastes pretty good, but filtering water makes a noticeable difference. The first couple gallons from this filter were gray with fine charcoal silt, but that's to be expected. No inconvenience there. Water from this filter tastes delicious -- noticeably better-tasting than from my Brita pitcher with a fresh filter. The difference extends to coffee -- the other major drink in my life. I like dark coffee that's at least a bit bitter, and I'm ever-so-slightly bummed that this water produces the taste that most sensible really like -- what we tend to call "fuller-bodied, etc." This doesn't qualify as an issue with the device, and after all I can use unfiltered tap water to make my bitter coffee.

Why four stars? First, I want to emphasize that I'm 100% satisfied by the filtering and usability characteristics of this thing. While it's not top-heavy, it's not bottom-heavy, either. Putting it in a location to fill a tall vessel like a pitcher has tipped it over a couple times. Because the housing looks like three sections of PVC, I've figured I could glue a flange to the bottom to address this issue. After a week of pretty heavy use (it's summer and my family's thirsty...) I can't say I've been frustrated by this, but have thought "if I were to improve one thing about this device it would be its balance."