This isn't the specific Uniqlo jacket you are looking at, but here is a 3 year old thread about >my impressions of a hooded Uniqlo parka that is comparable to a Montbell Alpine Light down parka(I owned the Alpine Light jacket)
The Uniqlo stuff, including my parka, seems fairly high quality in person. One thing about the fill power, as I said in the post, I'm pretty sure Uniqlo uses the EU fill power scale, which gives lower ratings that the US scale. I can't recall where I got the info, it might have been from that actual tag on the jacket, but I determing my 680FP rated jacket was more like 700+ in US terms.
The parka was warm, but could have been warmer if the fit was more athletic. There's no draw string at the waist, which probably partly accounts for it weighing less that the MB Alpine light parka while have more loft(compared to my Alpine Light Jacket.) The loose fit at the bottom allows for some cold air to make it's way up. Also, the neck is not padded or tight fitting, which allows for heat loss that way. I've tried on past versions of the UL Down jacket being discussed, and the fit issues are about the same. Nice jacket in the store though, and for the price vs Montbell or Patagonia. . .