There are two elements here...It might be more than just savings.
Correct me if I'm wrong but one advantage of these bonds is that they protect the buyer against a rise in short-term rates, at least relative to using futures. The futures buyer is short the repo rate (and has to pay commissions, bid ask spreads and waste his time during roll overs). If that rises more than the market thinks it will, he is screwed. The huge duration bonds don't get hurt by this (as much), i think it even benefits (as the 10y gets killed, its duration falls so the duration ratio changes and allows the guy on the 100y to sell some and free up even more cash to retain the same duration exposure). I'm assuming that spike in rates hurts the middle end more than the long end assuming people didn't lose the confidence in the central bank (which should be most of the time)
On the other hand, if the back end implodes relative to the 10y, then the 100y will get hurt more. So its a trade off.
Is this correct?
Firstly, a longer-dated bond is mechanically going to have less sensitivity to various short-term phenomena, such as central bank actions, spot inflation fixings, money mkt rate fluctuations, etc. Obviously, since all these things can go in any direction, this can either be a good or a bad thing.
Secondly, I believe what you might be alluding here is the significant convexity of long-dated bonds. There is undoubtedly value there, but that's value for which the mkt is normally going to demand a certain price. Will the price in this case be right?