See, PU Leather is a synthetic leather with a poly coating which has very less thickness as against Pure Leather.
Its primarily used in making of shoes, bags etc. if you check it
> The finish looks glossy
> Its a good water resistant, and can be cleaned easily
> Good Scratchless material
However - yes basis the quality - PU or Art Leather gets sticky and hot during summers.
If you park your car for a fairly long time in summers - and go inside - yes you will feel the seats bit sticky, but as the temperature comes down with AC - the seats tends comfortable. Also the life span and durability over a longer term basis of PU Leatherette seat covers is much less, if compared with Pure Leather Seats.
Despite same PU Seat covers are still in much demand - thanks to pricing as it comes as almost 1/3rd of the price of pure leather seat covers and looks as good as leather seat covers in a brand new car.
A piece of suggestion - If you intend to choose Art Leather, suggest to go with reputed brands like Stanley, AutoForm and - and check in product with good thickness and density. An inferior brand or product with less thickness will last much lesser.
For more info - Refer: Best Car Seat Covers