I have asked a lot of questions about mechs in this site, every viability of them, and I even made spider mechs. I even created the "mechs" tag . All of them have one thing in common.
NONE of them are viable
First to note is the cost to create one. I doubt one would be cheap since engineers will have to think of ways of how to counter a barrage of solid sabbot from a tank so your mech can somehow withstand or dodge the attack, and that will cost a lot.
Second is... the weakness a mech posses, specially humanoid versions. Destroy the leg.
Third is range weaponry, tanks are the beasts in the battlefield because they could fire accurately AND pack LOAD of punch! Their center of gravity is so low that firing their cannons will hit the target almost 100% of the time (provided the target is not moving) and still withstand the following recoil the cannon gives.
Do take note that's just countering a tank, we have yet to consider the munitions of every.single.weapon that we currently have(fighter planes, rockets, etc etc), how can a Mech withstand these threats? Are they realistic? How much might that be?
Mechs wins in the rule-of-cool match against tanks but viability wise, its the opposite.
I think your mech idea might be more viable as a powersuit, like Iron man. But I think that's for another question.
EDIT: It may seem I have to give my shot on giving my answer to the "viability" of bladed Legs OR Cheetah legs, I'll be giving my answer for both, WITHOUT the knowledge or purpose of these legs.
- Bladed Legs Or Stilted Legs: On humans they pretty much increase the height or your jump, the distance of each stride, granting you more mobility than a normal human AND can maybe used as a weapon (though this seems a bit dangerous as it compromises the integrity of your legs) This might be addressed by creating the legs similar to this. These legs are just made from 3 main parts, the thigh, knee and leg (from knee to foot). The thigh and knee are connected by well oiled bearing enclosed and protected by the knee (sorry I can't give you a precise illustration about this mechanism).
With these legs, this wont be used at urban areas for rescue and civilian duties because the legs will always drill down concrete. It is best used though, on urban warfare and rocky areas. Desert (specially sand only ones) forest and swamps are its worst workplace as these legs might be more of a hindrance than a advantage because they might drill very deep in these areas, restricting the granted mobility of these legs.
My Personal Analysis:
These legs might be more successful if equipped to human cyborgs or as a powersuit. The users can be equipped with sub machineguns and grenades. Give the user light armor than can protect it from most rifle rounds. the cyborg or powersuit is not invulnerable though, so it may fall down after several shots by high powered rifle, explosives and machine gun fire but its added mobility might help it bring down a couple of human infantry men, and a well placed kick might incapacitate a tank, before being destroyed.
These legs however has several drawbacks:
Stealth: I can't seem to find a way to make these stilted legs to be stealthy, as they seem to drill holes on the ground each time the user steps, so the preferred usage of these units overall are ambush or full frontal assault. They might be best to be used as "take no prisoners" units, they are too, good in torturing humans for intel.
Turning: With the absence of feet, a quick turn is noticeable which might be a problem because veteran snipers might pick you with a single shot. I have not yet found any advantages of turning using your waist, so I'm going to assume that its better if the user will use the high mobility legs to dash forward, then jump turn to re engage enemies.
Costs: This might be debatable since a well placed jump kick dive can destroy a tank, then proceed to kill the infantry with its guns and explosives, however, the cost to built a cyborg to use these legs are neither cheap nor humane. Human transfer is the cheapest and best option because the brain can store at almost infinite information, and with the help of a computer, complex attacks might be possible. I do think that human flesh too will make the cyborg lighter, putting ceramic armor vests for protecting might increase the mobility of the cyborg because its armor is lightweight. So long as the cyborgs destroy an average of 2 tanks and maybe 24 infantry, I can say that this might be a viable approach
NOTE: Do take note I created a cyborg because I think large mechs will have loads of problem using this. Examples are recoil and weapon choice.
- Cheetah legs: IMO are the worst legs that you can put on a mechanized unit. Cheetah legs are slim to help cheetahs run at full speed. Slim legs for a mech however, reduces its grip for handling recoil. WE might create a mech, a lifesize cheetah mech that is capable of slashing its way around the battlefield with a retractable sword on its sides then maybe 2 rounds of armor piercing missles that can penetrate a tank's armor. BUT as long as we don't have a lightweight blade capable of cutting a human leg bone like butter then this legs are useless. Maybe for scouting purposes but, we already have aerial drones for that.
TLDR: Creating a mechanized unit with these legs, especially the stilted one, might sneak to be a viable idea IF certain conditions are met. They are still faced with the common problems a regular infantry men faces(mines, IEDs,etc...) , or even a tank. But these doesn't change the fact that their greatest weakness is handling recoil. Giving stilted cyborgs small firearms and explosives is the most plausible thing to make them viable for war.
They are restricted also for War use only, rendering them useless during peacetime. You can ride a tank on urban areas but you can't use the stilted legs, well maybe the cheetah can be a fast ride, so is a F1 race car.