Hello,
Have not heard much of Stag CNG, i guess its a Poland based company
They have only single Authorized dealer in Mayapuri, Delhi
Italian CNG Kits are what more popular and are known for better reliability in Delhi market
Lovato, BRC, Landirenzo, Greco are some of the popular names. BRC is even used in Factory fitted CNG Kits from Maruti Suzuki
I suggest to explore more details of Stag CNG Kit, if in case decide to go with it, else for some branded names - refer on this post on -
Popular CNG Brands
Hope should help !!