Asking if you'll be addicted to methadone is the wrong question to ask.
The only question worth asking is "is this the way to make my life better?".
Sometimes in life there are NO perfect answers, you've only got the least bad of a bunch of bad options.
I got on methadone for my heroin habit 3 years ago and I've never once regretted that decision. It's not for everyone though. It depends on if it's realistic for you to take another option and if that other option is likely to get you a better life?
Don't fool yourself into thinking the goal is to be clean. It's not. Being clean is a means. The end is to have a functional and enjoyable life. As much as you feasibly can anyway. Active drug addiction prevents you having that. Methadone is one means to treating it, and there are many others.
Now if YOU should be on methadone, that's a much more complicated question. It's not automatic that if you have a heroin habit that you should get on methadone instead, not at all.
For one. Methadone is probably better used for the more severe heroin habits, less severe opioid addiction is probably better treated by subuxone.
And neither option is sometimes best if you haven't had a habit that long. Sometimes it's better to seek rehab or a taper and get off opiates completely.