Good question. Oleg, that really depends on you.
The fiber optics draw the eye... with red being almost BLAZING to me and so strong I sometimes drop the hammer like its a red dot and not pay attention to boxing it in the rear notch. That has been bad. I use green to tone it down and yellow on bright days. The FO posts appear BIGGER than a standard black front sight because the focus isn't on the edges, but the glow.
Your shooting a carbine so I'm assuming this is a home defense, SHTF, 100 yard rifle so you can't go wrong IMHO.
I think if you want adjustability, then go with a FO sight you can change. Never pay for FO from a gun dealer. It's way overpriced. I use this site:
http://www.fiberopticproducts.com/Flourescent.htm
On an auto I break a fiber about every 2000 rounds. On an AR, you'll go farther. I use a torch lighter to melt them in. Never a usual flame lighter, it just won't be as strong or mushroom as easily.
On the other hand, I use green the most, so if she's a SHTF rifle the HiVis sight is stronger and a cheaper try. But if you can use red I don't think you will NOT be able to focus on it. You can buy a narrow sight and by using the torch "shroom" the fiber to either thick or thin.
So..if it were me...(and many of my pistols wear FO)..I'd go with a FO post that I could change out whatever the cost because I use my AR for home defense. I'd start with red and then try green. The FO is brighter than the Tritium in good light, so if you can't focus on the FO then you're left with electronics....
After that, if she's a home defense gun and you want "always on" and "always ready" you need to buy an Aimpoint and leave it on all year (since the new batteries last like 5 freaking years).
Guns are so personal, I hate giving ANY opinion, but that's my honest truth.
BTW, I just turned 35 and I noticed I have trouble changing focus during IPSC matches. I may naver make Master in IDPA (I'm Expert), but I really like the fiber optics.