That's alright.
Yes, UDIMMs can be obtained at a relatively lower price but the problem with it is max you can upgrade is 24GB** while you can upgrade upto 96GB with ECC Registered (RDIMMs) memory.
Note: UDIMMs and RDIMMs cannot be mixed.
So based on the memory you need, you can make a decision but you had mentioned in one of the earlier post that your existing memory is same as the memory in the link mentioned in the original post (OP). If that is the case, which means your existing memory is ECC Registered and hence you will have to remove ECC registered memory to accomodate the UDIMMs as they cannot be installed simultaneously.
Imagine you go with 24GB of UDIMMs but in the future when you need a memory upgrade, you will have to sacrifice all the UDIMMs just to make way for the RDIMMs which is nothing but wasting a reasonable amount in between the tiring process.
So wave your options and go accordingly. If you were me then I would go with RDIMMs :
1. as it the same memory which is currently working fine in my system
2. the extra memory upgrade capability which can be of a great use in the server environment.
Goodluck!!