Baby Milk Bottle Steriliser vs Steamer

My MIL passed down to me baby milk bottle that she kept for 4 years (I supposed it's 4 years as my husband's nephew is presently 4yo). She said can just replace the teats. 1. Isit advisable that I buy brand new bottle and not just replace teats? 2. FTM here. Is the attached picture - a milk bottle steriliser or steamer? 3. Which one is better - milk bottle steriliser or steamer. Why? TIA.