I looked at the first one on the list and I saw this in the details.
Copyright (c) 2021 by Riley Adair (https://codepen.io/RileyAdair/pen/ZvyYzr)
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
It says its free as long as you display the copyright notice in full. I imagine the others are the same but you will need to refer to the details page on each codepen or demo.
If they do what you want, and you have stress tested in various browsers, and if they meet accessibility needs then they should be fit for purpose
All the time. There’s no need to re-invent the wheel when you know a code block is good and has been tested thoroughly.
It depends on what you are building.
The problem with all these sliders is that they often cater for every eventuality and the code is therefore quite bloated if all you wanted was a simple fade that could be done in a few lines of js (or indeed in css only). However when you start adding various animations, captions, mobile screens, responsive images, keyboard access, tabbing etc. then you are better off using something that already does those things properly and efficiently.
The slick carousel is one that gets a lot of recommendations.
Yes if you can find a slider that does what you want and is optimised towards your goals and has no restrictions on usage then it may make sense to use it. Make sure though that you more or less understand how it works otherwise you won’t be able to fix it if it goes wrong