I like this series a lot: the sex scenes are pretty good compared with the average explicit yuri hentai.
For the most part, the sex acts they do seem actually pleasurable for the aunt. How many anal scenes on this website include clit stimulation as well?
Positions are generally feasible -- eg when they fuck in ch2 with the aunt sitting on the bath rim - most yuri Hentai in the bath has them lying in top of each other which doesnt seem comfortable at all. Little details like the niece washing her soapy hands before fingering the aunt make all the difference.
Its written from the POV of the bottom, which is kinda rare for the super explicit stuff (most of it is from the POV of the top, or "voyeuristic"). I like that their dominant/submissive dynamic has an emphasis on teasing, which is also kinda rare.
Its not perfect - the art could be better, and I prefer more realistic body proportions. But this series gets a lot of things right that most (very explicit) yuri Hentai doesnt.