One of the primary advantages of wire cages is that no matter how much your degus chew, scratch climb and wee, the metal is very robust. The cage is immune to chewing and mostly immune to damage from the outside (should you drop it during transportation for example or knock something heavy into it).
Although most second hand animal cages seem to have a low resale value its often the case that it is easier to resell metal cages than wooden ones.
More immediate access to animals
So in a metal cage it is quite easy to interact with the animals inside without having to constantly open a door/front. If it is important that you can poke your fingers through the bars or offer treats then having a metal cage is certainly a bonus.
It is also the case that in a metal cage it is often much easier to see and keep an eye on the animals inside due to the fact that the metal cage provides open viewing points from all angles.
Objects and accessories.
In a wooden enclosure, every time you want to attach a secure or permanent feature you have to screw another hole. In a metal cage you are able to attach wheels, branches and ropes to the bars of the cage easily and securely without the possibility of damaging the integrity of the cage - meaning you can rest easy!
Natural themes
Although not as easy to recreate a natural aesthetic as would be in a wooden enclosure I do feel like I should include this point as an advantage to both wooden and metal cages. Should your cage be of the appropriate size or bigger it is possible (with a little extra effort!) to create a pretty good looking interior. Winic from the Deguworld forum has achieved a lovely looking interior...
Short term cost effectiveness
In the short term metal cages are quite cost effective. Compared to wooden enclosures they are cheap to buy and very easy to find.
If you find yourself adopting degus at very short notice or perhaps an unexpected litter from a pregnant female occurs, it may be the case that you need a space for them ASAP. Now it should be said that all degus should be kept in the correct size enclosures from the earliest available time, but sometimes it is not possible to purchase or build an enclosure large enough due to fund restrictions. Under these circumstances it may be more practical to use an old metal cage or find a second hand one cheap until such times that the cage can be modified into a bigger space or new housing is available.
But remember, as an owner you should always be looking for ways to improve your degus environment, so a metal cage that does not meet the specifications should always be considered a temporary solution.
I would also like to reiterate that in the long term, a metal cage cannot beat a wooden/custom enclosure in terms of sheer value for money.
Additional assorted benefits
Well ventilated. No problems here when it comes to the concerns of ventilation.
Metal cages are easier to cool during the summer (but remember to keep away from draughts!)
Metal cages tend to be very light compared to their wooden counterparts.
Good for introducing new groups of degus. You can easily place the cages close enough that the degus can see and smell each other without the opportunity for any physical contact.
A final word on Metal Cages
As a community, our knowledge of our pets has increased greatly. It is now generally accepted (by a large percentage of the online community of various forums and websites) that there are no commercially sold cages that are suitable to a degus needs.
All metal cages will require some form of modification, I.E; expanding half levels into full levels, combining cages to make larger cages or perhaps providing a run that the degus have constant access to.
Providing detailed guides on how to construct and build degu enclosure, vivariums and cages. This blog has a focus on stimulating and creating more natural habitats for degus...