Thanks Hog!
I have done some research (thanks FrankTalk forum) and now have some views on the RTEs (rear tip extenders) that may help guys confused about this. My conclusions are based on a number of contributors here (search rear tip extender), but also this scientific article on RTEs (which includes Eid as an author):
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6559880/To start with, you need an implant that fits. Sizing up or down is bad either way… you either end up with floppy glans if you size down, or erosion if you size up. Both are bad… search the forum if you want to know more.
If you are 24cm, you need 24cm of implant, whether in the size of the implant itself or any RTEs that get added on to the end to make sure it fits. So if your implant is 21cm, you need 3cm RTE to get you to 24cm.
Your length is measured in the operating room after they, uh, open you up, so you don’t know in advance. And before any of you guys think I’ve been blessed with a 24cm dick (9.5 inches!), note that the length is the combination of your external (distal) and internal (proximal) sizes. A rule of thumb is that your internal is about a third of overall length, so I’m really quite normal.
Different implants come from the manufacturer in different sizes. The AMS CX comes in 12, 15, 18 and 21 cms. But! Apparently you can special order a 24cm.
So you take the biggest one that fits and add RTEs to fully fill the corpus. In my case I had 24cm to fill, and I suspect I got 21 + 3 because my doc didn’t have a special order 24cm on hand.
The vast majority of implants come with RTEs. Per the study I linked, about two thirds of implants have an RTE. But that varies from 73% of implants by low-volume surgeons to 58% by high-volume surgeons.
The presence of an RTE is correlated with an increased risk of complications. But it’s not exactly clear why that is. There could be intervening causality given that low-volume surgeons do most implants, and are much more likely to do the one’s with RTEs (note to researchers: why not easily compare the rates of complications controlling for things like provider volume? Seems like statistics 101 to me). Another factor could be something like what may have happened with me: the doctor simply didn’t have a 24cm implant on hand.
The other anecdotal and theoretical complaint is that RTEs, since they don’t fill with fluid, push out the “fulcrum” point of the inflatable to malleable portion of the implant. The study authors described it this way:
“The point where the inflatable component meets the malleable component of the implant has an impact on the implant’s performance. This point can act as a fulcrum, allowing the implant to flex even when fully inflated. The use of longer RTEs advances this focal point more distally in the corpora, which then changes the angle of the erection, and thus decreases the quality of the erection. In a natural erection, this focal point would be at the proximal end of the corpora, at the crura, which are fixed. This phenomenon is similar to what has been described by patients using a vacuum erectile device and a penile ring, where the penile ring acts as a fulcrum and only the corpora distal to this is erect. Patients complain of a “floppy” erection in this situation, which is hinged and thus not become erect as one contiguous structure.”
Some of the really high volume providers describe “tricks” they have to cut down on RTEs. Some carve them off, for example. One benefit is having a large range of sized implants to choose from. And I understand some docs might use Doppler to estimate the size beforehand, and talk to patients about using Titan or AMS (which come in different sizes) depending on what they find in the operating room.
Whew! That’s a lot of research for the afternoon after my surgery. Here’s the TL;DR:
• The vast majority of implants have an RTE.
• RTEs seem likely to have some downsides, but it is unclear just how significant they are.
• You are more likely to be one of the minority without an RTE if you use a high volume provider, but still likely to get an RTE.
Leto
However, I was floored at the total estimated cost: $72,000! 
That's way more than what I've seen here on FT. Thank God for Medicare!