The best thing is to use sat/vbyte to avoid any confusion, so atomic wallet still using the sat/byte is already a red flag to me to stop using them
I really don't think that it's a red flag. Although I haven't made use of atomic wallet before I'm certain that picking a suitable fee for your transaction depends on the users understanding of the mempool and congestions , as well as if the wallet allows full customization of fees.
After this correction you and _act_ made I decided to look it up on the forum and here is what I found;
sat/byte
This means that for every byte your transaction is, you'll pay the analogous satoshis.
sat/WU
“WU” stands for “weight units”. After the SegWit activation in 2017, it has replaced bytesize as a measure of how much space transactions take when put into blocks. While a block can be up to 1MB, its weight is 4 million WU. Using SegWit reduces your transaction's WU size.
sat/vByte
For legacy transactions: Byte = vByte. One virtual byte is equal with 4 WU. Essentially, sat/vByte tells you how many satoshis you'll pay for every 4 weight units of your transaction. Obviously, it'll be reduced if you're using SegWit.
You should read this:
Weight unitsIt turns out that the calculations you make use of really doesn't matter as long as you use the right values for the transaction. Most wallets make use of sat/byte for their calculations as a default unit.