I cant comment specifically on the GS in the
L39(never use one) vs the HST in the
L45 but I do have the HST in my
B26. I like being able to leave the tractor in gear when digging with the backhoe and then (with aid of a rod stored on the backhoe) reach the HST pedal and move the tractor any amount needed from the reversed seat. I don't think you can do that with the glideshift transmission but I could be wrong.
My HST while bringing you to a stop if you suddenly remove the pressure from the pedal, doesn't snap you forward, rather it comes to a stop similar to braking with a gear drive. What I really like about the HST is that you can control all the forward and back motion and speed with on foot which leaves both hands available to steer and use the other hydraulic levers. When reversing with my LS (gear drive) it takes one hand (and one foot) to move the reverser and lets not forget about braking also so there goes the other foot, one hand to raise the FEL, one hand to lift the 3 PH, shucks forgot I only have 2 hands so something has to wait on the other to be performed AND forget about steering at that time (4th hand option). While all this can be done at almost once with a lot of practice, it is just so much easier with HST.
My suggestion is to operate both tractors and decide for your self if the extra money is worth it to get HST over GST, particular attention given to moving the tractor when using the back hoe. It does take a cane/stick or other apparatus to reach the HST pedal to move the tractor with HST but it can be safely moved and steered from the backhoe seat.
NOW my Kubota RTV will give you a windshield hugging experience if you abruptly remove your foot from the accelerator as it will lock the wheels into a stop so it is a new learning experience to drive it.