I upgraded to S20FE from A8 plus and I personally feel its a good phone. I got the 5G version so I have the Snapdragon 865 processor which really is good compared to the S20 plus which has Exynos 990 processor.
I personally feel the S20FE feels much better on the hand compared to even S20 plus because with the S20 plus you can really feel the plastic back but with the FE because its somewhat matte finish it feels much more premium though its just plastic.
Comparison with A8+ and S20 series
After I held the S20 plus for the first time I honestly didn't feel like it was an upgrade from the A8 plus mostly because it felt much more thin and I could mostly feel the plastic back instead of the metal sides.
Comparison with IPhone 12 series and S20 series
IPhone 12 and Iphone 12 pro felt much more premium as in the body was completely metal and the design is much more grippy so it was easier to hold it in my hand though it did feel like a brick at first.
I personally feel that Samsung should really include a full metal body instead of adopting the plastic back for premium phones. For A series and below having a plastic back is ok but for flagships like the S series and the Note series should go for the full metal body. I held the Note 20 Ultra and it really did feel premium, also it does feel like you really paid a lot for the phone. For me when I upgrade my phone I want it to feel like an upgrade thats why I went for the S20FE instead of the S20 plus for three reasons firstly in my region S20 series comes with Exynos processor instead of the Snapdragon and second the S20 plus felt cheap and finally S20FE 5G was much cheaper than the regular S20 and had Snapdragon.