"With me or with Duo."
Translation:Benimle veya Duo ile.
They are two different grammers 1) "la/le" means with/and 2) li/lı/lü/lu is sort of like the "y" we add in English to transform a noun into an adjective Peynir means cheese Peynirli means cheesy Peynirle with cheese To illustrate more Sütle pasta yerim (here you eat cake and drink milk with it - cake and glass of milk) Sütlü pasta yerim (you eat milky cake / cake with milk inside it/ cake made with milk) I hope this is clear in any way
The instrumental case takes the 2-way vowel harmony:
(a, ı, o, u -> a) and (e, i, ö, ü -> e)
You can't have 'Duoylu'. It is either -(y)la or -(y)le. Following the rule you have 'Duoyla'.
Do not confuse instrumental case with the “with” or “without” whereas the suffixes are -lI and -sIz, which follow the 4-way vowel harmony.