I have found many advantages to having slide mounted safety/decocker levers and some obstacles in using frame mounted levers.
While there may be some designs that have had problems (such as early M9s, Beretta model 92s) such as accidental activation of the safety during racking, even current models have a better lever angle now.
Obviously, I have extensive experience with the PX4 line which has excellent levers and 6 options of lever configurations (not to mention mix & match). Stock PX4s have levers designed for gloved winter or harsh condition activation, but most folks now run G model (decock only) with smaller, less sharp levers.
Advantages of a slide mounted decocker/safety? Firstly, mechanically an accidental discharge by decocking becomes impossible. The same metal lever shaft that decocks cannot do so until it physically moves the firing pin plunger out of the way. The hammer will also hit the back of the slide, not a catch or stop, nor the sear.
Secondly, I do not have to alter my full shooting grip with either hand on either side to decock or run a safety, if applicable.
Since this does not show that frame mounted safeties are less safe... that is not my point.
When shooting I find certain obstacles that I don't think "need" to be there.
Slide mounted decockers (like Beretta's) are ambidextrous. Some frame mounted levers are also, but at a different cost.
When decocking or coming off safe with frame mounted ambidextrous levers the other side hits your other hand and you must loosen your grip to accommodate. You must also loosen your grip to lower the lever you are using.
Grip is my main gripe. I like to run my thumbs high, almost up to the slide. So, one must go on top of the levers and risk decocking during recoil... On the levers and risk wearing out your thumbs or under the levers, which makes for a lower grip more below bore axis.
With grip mounted decockers, like a traditional Sig- I find I must release my grip with the support hand to decock and find no easy solution if firing lefty.
While necessity is the mother of invention and techniques can be developed for any type of manual of arms... I find that slide mounted levers (when done right) are better for me. Yet there are so many strong feelings and views against slide mounted levers that I thought this would be worth discussing.