i like mine....mine is a 20* and at this point, if i need a bag for colder weather, i will probably get another slick bag (0*) i like not having to worry about it. yesterday morning i woke up pretty wet, but it wasn't until the alarm went off that i found out. i live in a wet environment, and i'm hard on stuff... it's bulkier and heavier than a good down bag, but life is full of compromise.... slick bag is a practical option for me.
i have had mine to 26* which gave me confidence it's a true 20* bag for me, because i was plenty warm, and wasn't wearing much clothes. i have some down jackets, and i know i don't like down in really wet conditions. just because it's a good choice for me doesn't mean it will be the best choice for you, but i like mine a lot, and have no plans of changing.... it does exactly as i ask.
when it was 26*, i had to unzip it a little because i was getting too warm around midnight, and woke up comfortable at 4am still.... i was also sleeping in the bed of my pickup which is colder than a shelter. it was also pretty easy to dry yesterday, which is confidence building.
i have slightly different needs than most in my sleep system, i am mostly in mild temps, and is catered to wet conditions. when it was cold last week, my pad had a 4 r-value, so i have some room to get colder temps out of my sleep system. i think i could go down to teens with a warmer pad and wearing some more clothes.
i think the slick bags are plenty accurate on their temp ratings