I moved into a one-bedroom in a building where the previous tenant had clearly cooked a lot of curry. Beautiful food, but six months of it had settled into the drywall. My first three weeks I tried two cheaper purifiers and a lot of baking soda. Neither did much. The Alen 75i, running on the Fresh filter, had the apartment smelling neutral inside forty-eight hours.
That is what this machine is for. The Fresh cartridge carries about three and a half pounds of pelleted carbon, which is a stupid amount of carbon for a home purifier, and it shows up in the only test that matters: things stop smelling. Cooking, the cat's litter corner, the off-gassing from a new IKEA dresser. All of it fades into the background within a day of running this thing on auto. If your problem is particles, a cheaper Levoit will keep up. If your problem is your nose, this is a different category of device.
It is also genuinely quiet at the speeds you'll actually use. I run it on speed two overnight in a 12-by-14 bedroom and I cannot hear it from bed. The laser particle sensor is accurate enough that the auto mode picks up cooking from across the apartment and ramps up before I do. There's a satisfying logic to opening a jar of vinegar and watching the light on the front turn amber three seconds later.
The app is the part that made me laugh. It exists, it connects, and that is about all I can say for it. There is no way to adjust auto-mode sensitivity, no useful history view, no scheduling that I trusted enough to use. After a week I stopped opening it and just used the physical dial, which is fine because the physical dial is fine. If you were buying this for smart-home choreography, you'd be disappointed.
The other thing is the size. This is a big appliance. It takes up the floor space of a small end table and it is not pretty. I have it tucked into a corner behind a chair and I have stopped noticing it, but for the first week I kept catching it in my peripheral vision and thinking somebody had left a piece of equipment in my living room.
The lifetime warranty is real but it comes with a leash: you have to register the unit and you have to buy Alen-branded filters. Third-party PUREBURGs cost about a third as much and will fit, but the warranty evaporates the moment you put one in. Over a decade that's a real choice — generics save you a couple hundred dollars, the warranty is presumably worth more if anything ever breaks. I went with the genuine filters and I am hoping I will be smug about that someday.
At $799 it is not a casual purchase. The Levoit Core 600S costs less than half as much and will clean particles out of a bigger room. What it will not do is touch the smell of last night's salmon by breakfast. That gap is the entire reason to buy an Alen.
Verdict: Buy this if you have a specific odor or VOC problem and you've already tried throwing a cheaper purifier at it. If you just want clean air in a big room, the Levoit Core 600S does that for half the money.