I currently show and lesson/jump my horse in a segunda. He seems to go very well in it and has been going in it for 6 months or so now. However, when I am just hacking on my own I try to use something a bit softer so that I don't have to keep bitting up and for variety. It seems to help him respect the segunda more. Right now I hack in a eggbutt french link snaffle which is simply not quite enough bit for him. He has a tendency to get heavy in my hands with this bit. I realize that bits are not a substitute for good training, but would love some suggestions for something in the middle that might work a bit better.
My eq. horse/back up hunter shows/jumps in a custom segunda pelham (the port rotates 360 degrees and the shanks are fixed) with a chain nose band. He is a 17.3, 2000 lb Dutch WB built like a Cadillac limousine...there's not much else you can do! Point being, at home he flats in a slow twist loose ring gag. It's a GREAT bit for him and it's just enough without being too harsh. Might be worth a shot!
Nine out of ten times, you'll get it wrong...but it's that tenth time that you get it right that makes all the difference.
That is the one I use, with keepers to prevent it from rotating onto the tongue too much; I find the keepers dull the effect a bit because of how they hold the angle of the mouthpiece. It might give a bit similar feel to a segunda while not being quite as sharp. I like using it occasionally on a horse who likes to pull out and down. Being small, it is difficult to be pulled on and frankly life is too short. I use it for hacks or occasionally for schooling sessions. My everyday bit is a copper single joint snaffle with dropped noseband.
Another option might be a dropped noseband over the french link or dr. bristol bit. Although that is more useful with a horse that pulls down or gapes its mouth to evade. Another note: I have yet to have a horse that went well in a slow twist bit. Just my experience.
I guess it depends why you use a segunda. I jump my hunter in a jointed segunda because she can get really strong at the ends of the ring particularly after the change. I don't touch the bridle in the show ring really except when she gets strong. Other than that she has a very soft mouth and hacks in a jointed happy mouth. I've also ridden her in a Waterford.
Do more transitions in your schooling. Work in shoulder in on the wall every ride. Work your trot halts on the wall. Make them prompt off your seat. You should be able to push the nose forward as you transition downward.
I've never met a horse I've had to 'bit up' and I've been at this professionally and as an ammy for 30 years. School to better balance