The word tradeoff is not listed in Google nor in CantoDict.
Is it 折衷?
What's the Cantonese translation?
What's the Mandarin translation?
1 : a balancing of factors all of which are not attainable at the same time
2 : a giving up of one thing in return for another : exchange
Trade-off as a noun is 代價 in both Cantonese and Mandarin ('trade-off' basically means "in exchange" )
"Thicken the armor would provide better protection, but the trade-off is your speed would slow down."
You can use "作為交換" (in exchange) instead of "代價是" e.g. "加厚护甲会提供更好的保护，但作為交換, 你的速度会减慢。"