Choosing the best metal trundle bed involves first being sure the bed is large enough for your needs but small enough for the space in which you intend to place it. Versatility also is a consideration, and ensuring that the chosen metal trundle bed can be used close to the floor and raised to the height of the bed to which it is attached can give you that versatility. You also likely will want to consider the durability the trundle bed, paying particular attention to the construction of the metal frame.
You first should make sure the metal trundle bed you choose is the right size, because it needs to fit comfortably in the room in which it will be used. This means you should measure the space you have available before you buy the metal bed frame so it does not take up the entire room, especially if you plan to keep the trundle bed pulled out a majority of the time. In addition, the bed should be large enough to fit anyone you expect to sleep on it. Though most trundle beds tend to be no larger than a twin bed, because they need to be smaller than the beds under which they are stored, you may be able to find a larger size if you need it.
Another detail to think about is whether the metal trundle bed you choose can work in various positions, because the best beds on the market tend to be versatile. For example, you should be able to pull out the trundle bed and leave it on the floor so guests can sleep next to the bed under which it was stored. Many types of trundle beds also can be lifted up to the same height as the main bed so you can create what appears to be a larger bed. Some metal trundle beds even come with holes drilled into the frame so you can add a headboard and footboard if you ever wish to turn it into a bed that stays out permanently. If you think you will use the metal trundle bed often, then this may be a good option for you, especially since buying a bed with a trundle usually is cheaper than purchasing two separate beds.
An additional concern should be the durability of the metal trundle bed. Many of the most durable trundle beds on the market feature metal bars across the bed to ensure that it is strong enough to safely support anyone who sleeps on it. You are, however, encouraged to find out if there is a weight limit associated with the bed you want so you can make sure that you the bed's maximum weight is not exceeded. When possible, you also should test out the strength of the bed by sitting or lying on it to make sure it feels sturdy enough to support you, whether it is on the floor or raised to the height of the main bed.