I suppose it depends on what shotty you are mounting a side saddle on. Final use also dictates which unit will work for you.
Generally I find that a receiver mounted side saddle fully loaded with buck/slugs tends to torque the receiver to the left. Not a big thing unless you are carrying it for hours on end or trying to hold a firing position for some time.
The
slip ons tend to catch on brush, etc. It's only a matter of time until the elastic stretches and then it drops shells or falls off the stock.
Sling/bandoleer combos add a lot of weight and suffer from the same problems as cuffs in that the shell holders eventually stretch. They also suffer from being catch magnets for anything they can snag on.
TacStar uses plastic to make theirs and they work for a while. A popular option.
Mesa Tactical uses an aluminum base plate and mount more securely. They have redesigned some models to add a picatinny rail, which might be useful, but loaded they still torque the receiver. These are probably the best made of the bunch, however quality always costs extra.
Another option might be a
bandoleer. The elastic shell holders are sure to stretch after some use. 50 shells might also be over kill, unless its a war. Another factor is that they are separate from the weapon, especially at o'dark thirty.
Some trap/skeet shooters use a fanny pack/
pouch to hold extra shells at waist level. Practice would help you here. Again seperate from the weapon.
I prefer the pouch/fanny pack for extra ammo. Packs aren't as convenient as weapon mounted but probably will last longer in use.
Here's a nice
write-up on using Velcro to mount a side saddle to the receiver, making it quickly removable.
Whatever you decide, practice makes perfect, as they used to say.
A note on
Ace Case products. I have no financial ties to Ace. I have used their cases which I find to be very well crafted and a quality American made product. Just my experience and opinion.