I have actually used most of these tweaks, at one point or another, but no longer jailbreak.
Callbar is about the only one that I can agree with the OP on. It is rather ridiculous that, when a call comes in, it takes over my entire screen. I actually use my phone with clients and, while it hasn't happened more than maybe twice, when a call comes in, it effectively boots you out of the app. Now that I have a son who is learning to talk, it's entirely possible that my personal phone calls will be more frequent.
As for everything else...
Swipenav - I have always been a two handed user for easily 90% of tasks. Even when my phone was a measly 3.5". Navigation is a non-issue for me. But you still don't need to reach the top of your screen with the iphone 6... just double tap touch ID. For me, a non-issue.
Deleteword- Not to sound pretentious, but I don't find myself typing entire words and needing to delete them. Soemtimes I will rethink a sentence, but since I have always been a two handed user (mentioned above) I just select the sentence and delete. I can't say that I would hate if this was implemented into iOS, but I don't need it, personally.
Zephyr- Closing apps is faster. I won't argue that. But I also don't really close apps all that often. The only app I close consistently is the maps app (to kill navigation once I know where I am or have arrived more quickly). I certainly can;t justify going through the hassle of jailbreaking (I will talk more about why i consider it a hassle below) for this feature that will save maybe a second out of my day every once in a while.
Sleipnizer- This is one I haven't used. Sounds pretty cool. I might put this up with callbar, had I used it. I can actually see myself using this seeing as how I do do a LOT of web browsing on my phone. Perhaps I will try it out on my iPad mini which is jailbroken, but is currently collecting dust since I got the 6 plus lol.
OpenTabBG- Since I haven't used sleipnizer, I can't REALLY comment on this, but the "inconvenience" of holding down a link has never really been noticable to me. I dn't find it all that hard to hold down a link and I don't find sensitivity to be an issue. Maybe when I try this on the iPad it will be some night and day difference, but I just don't percieve this as an issue in need of fixing right now.
Shaketoundokiller- Shake to undo has been an issue maybe a half a dozen times since it's inception, for me. It's not a feature I find myself using, nor is it one that I am "constantly activating accidentally".
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Now lets talk about the problems of jailbreaking. First and foremost, updating is a pain. Not only do you have to wait, but you have to do extra work to restore your device the way you wanted it. Yes I know you can make backups, etc. It's just more of a PITA than OTA. Back when updates were iTunes only, it wasn't as big of an issue for me.
Then there is the issue of stability. Apps and tweaks from the cydia store tend to have more stability issues. I can;t tell you how many crashes I have endured (although my 6Plus stock has had some crashing as well, so that point may be becoming moot lol). True, there are many stable tweaks, but I need to weed through them and find what works for me. I am not a college kid anymore that goes to class, plays with his toys, and then goes to bed (those were the days). Simply, I don't have the time to poke around my devices and get them running "just so".
Battery life also seems to suffer. Maybe this is in my head, But even running the most minimal number of tweaks seems to cause an adverse effect on my battery life. perhaps with the 6 plus, which easily lasts me the full day, this wouldn't be a sacrifice at all. I really couldn't say.
Security is my last, and now biggest, concern. No I am not some paranoid guy that thinks cydia is some place where crooks come to install unsigned packages to your device and steal your identity. But we are storing more and more of our lives on these mobile devices. Fingerprints, credit cards, etc. are all things I didn't need to even think about a few years ago, but now I do.
So I guess the bottom line is that jailbreaking doesn't really give me any killer features like it did 3+ years ago that makes what I have to potentially "give up" worth it. That isn't to say that I am not extremely greatful for how, IMO, the jailbreaking community has causes iOS to grow. That alongside Android pressure got us a ton of features that I think we still wouldn't have in iOS to this date.
