Every phone needs case which is designed for it. I will be limited to products/brands which are available in stores in my town.
You can always order online through a manufacturer's website, or search sites such as Ebay or Amazon for something specifically designed to fit the phone you have.
For example, this one person I know purchased this case off of Ebay for less than USD$15 (that's including shipping costs). Don't let the price fool you; a lot of times, these sellers buy their stock in bulk, so they are able to sell them for really good prices. It is a 2-part/2-layer case that is thin enough that it easily fits in his pocket but that also protects his phone quite well (which is good for him because he has a tendency to drop it at least once or twice a week
I will probably buy successor to Lumia 535. For Lumia 535 I found cases without detailed description which cost $10-$15, but it isn't clear if some of them can really protect $110 phone.
If the case is not advertised as being "rugged" or as being made of silicone, it's not going to provide the same amount of protection for your phone if you drop it. Both of the cases you have linked are "flip cover" cases, and upon looking at them, they're just made of thin plastic. They'll provide some limited protection from scratches if you put your phone in your pocket and also have your keys/loose change in them, but if you were to drop your phone, they'll probably do nothing. I have seen several of my students using this type of "flip cover" case, and yes, a few of them have dropped their phones, and all of those phones suffered damage (cracked/broken screens).
It is possible that phone with case won't fit into pocket or it will bend. I won't do drop/bend tests and there are probably no videos.
Unless you make a habit of wearing pants that are "skin tight" on you, the majority of phone cases (even the rugged/silicone/"bulky" ones) out there are designed so that they can fit into your pocket. The few that cannot are usually the ones that have/use a belt clip (like the one I have) or they tell you that if you use them, you should be keeping your phone in your purse. As far as whether or not it will bend, well that's not really an issue of the case, but rather, a problem with the phone itself.
In the end, it is your choice, of course. After all, it's your phone that you want to protect. When it comes to cases, there's a bit of a trade-off that you must be willing to accept when you're looking at form (usually "Do I like how it looks?"
or "Will fit in your pocket?"
) versus function ("Will it protect my phone if I drop it?"
). Just keep in mind that cases that are advertised as "slim" or "sleek" will likely fit into your pocket easier, but THAT is what they're designed for (i.e. they are designed more for looks/pocketability rather than protecting your phone from drops), so you'll need to be extra careful when you handle your phone. You can find rugged/silicone cases out there that will fit in your pocket, though you may have to search online instead of limiting yourself to what you can find in the stores in your town.