I assume the recommendation was for the TeleVue 31mm Nagler, not a Radian - the Radians don't have focal lengths greater than 18mm.
I don't know that I would call that particular eyepiece "ideal", although it's certainly superb. It's also just about as expensive as eyepieces get, so don't do this lightly!
The Andromeda Galaxy is a very large object; from dark skies it extends over 3 degreess (6 full-moon diameters)! From light polluted skies the dimmer outer fringes are much less visible.
The 31mm Nagler was recommended probably because it gives a nice low power and a very wide field of view. It shows a little over 2 degrees of sky when used in your scope. Also it gives slightly less than a 7mm exit pupil, which is usually the largest recommended. So, the 31mm Nagler, in your scope, shows as much sky as possible in one field of view without exceeding a 7mm exit pupil size. This is great for very large objects like Andromeda.
(What's the exit pupil? too much to explain here...but something to keep in mind as you learn about this. You can calculate the size of the exit pupil by dividing the focal length of the eyepiece by the focal ratio of your scope. In this case, 31mm/4.5 = 6.9mm.) Why a 7mm limit? This is about as wide as your pupil can expand. In many people, it's a good deal less than even this.)
That said, if you're asking about objects "like" the Andromeda Galaxy, there aren't all that many. Andromeda is the nearest large galaxy, and is therefore unusually large and bright for a galaxy. There are some other objects with large apparent sizes (a few large nebulas and open star clusters), and low powers are good for finding objects, so a very wide field eyepiece like the 31mm Nagler is certainly useful and desirable. However, I'd think twice before spending that kind of money at this point.
For someone first learning about all of this, I think a few good Plossl eyepieces and maybe a good 2x barlow lens is really all you need; then as you learn a bit more about observing you'll be better informed about what you, personally, want in a more expensive, premiium eyepiece collection. For low power views, a 25-32mm Plossl will do great, and cost a tiny fraction of the Nagler.
On the other hand, if you have lots of money, the 31mm Nagler is great, although I might lean towards the 26mm, but that's my personal taste (I get some funny little optical effects from my eyes with very large exit pupils).
