It is hard to know if the strings are worth replacing. Usually I get more of an upgrade from trying different bridges of various types of wood, shapes, and height. The strings do wear out over time. If the erhu is used or shopworn with corrosion on the strings, new strings can be a good idea. It is reasonable to try something different at times, since new strings are relatively inexpensive and installing not so hard after some practice.
I have tried a variety of basic and expensive strings for erhu, and have returned to basic and inexpensive strings such as Dunhuang/Mudan. Currently, my favorite strings are relatively inexpensive Huqiu brand. I have not tried D'Addario strings. From the Ebay listing, this is D'Addario's first foray into erhu strings. I suggest that Dunhuang, Mudan, or Huqiu strings are plenty good for a student erhu at least, but I don't have anything bad to say about more expensive options, such as D'Addario.
It depends on how much your erhu cost. The supplied strings should be perfectly adequate in all except the most budget erhus ( and these are probably unplayable anyway).
My first choice are Huqiu and then Dunhuang, both are very cheap. I've not experimented with more expensive strings. Easton's website has a good section on string selection.
Ed
ps. I seem to remember my Lu Lin Sheng and Hu Han Ru came supplied with extra Huqin strings, so I continued using them.
I shall take a look at these strings brands and see if they are what I already have as spares. Unfortunately my erhu is a very budget erhu as it was bought as a surprise gift by my husband, and he wasn't sure if I would like it - I think it was about the $70 range. He got it from someone in the UK, so it was already imported.
It does however seem to be playable. It was sounding very grim but I have improved and done some upgrades! Swapping the disintegrating foam dampener for a nice wool one and changing the black bow hair for white have both helped massively, I was quite shocked as both of these changes cost me less than £10 including postage to do (although changing the bow hair was a challenge). I shall have a look at ordering some different bridges next.
It does sound more like a violin at the moment, rather than having the mellow weeping sort of tone - I suspect the this is due to the quality of the wood and snakeskin, but I expect my novice level also plays some part in it.