It depends on user expectations I guess. I have no complaints on the UI and speed of the interface. It is not the fastest, but I am not using it for games or apps like in iphone, and probably people compare its operating speed vs a iphone.
My AK Jr does not hang on me, does not stop playing all these time when using. It just took longer to boot up, and after that, it is all good and smooth. It is a lot smoother and faster than most high end China made DAP that I used to own.
I have literally all music files with album art all working perfectly. Something that all my other DAPs couldnt do at first time.
Try out an actual set and make judgement call if it fits your requirement. Some find it a slight lag, but some, like me, finds it very acceptable. Perhaps it is my personal experience with other DAP that are really slow, as compared to my AK Jr. For me, a DAP will just be required to display the album or songs categorised properly, I scroll to the choice of selection, it reacts smoothly with the right song. Click play and it plays. If need to change songs selection, click next button at the side, and it immediately change to next song. Rest of the time, the DAP should deliver the best sound quality possible. This will be what AK JR perfectly delivers.
Always happy to see new firmware out to make it even better for user experience, but I will be perfectly happy to use it if no more improvement in the firmware.