Thermo bottle for impromptu sous vide? I would like to try out sous vide, but I don't want to invest in the gadgets, until I have tried it and decided I want to keep using it. So I have thought about the best way to try it with no budget. Online, one of the method suggested is to use a beer cooler and zip bags. Would it also work to use a thermo bottle (a bottle, which keeps your tea / coffee warm) for this? I recently used my thermo bottle for 12 hours+, in the winter, and even after 12 hours it provided fairly hot tea. Would this work or would it be too small as container? I am pretty sure, that it could hold the temperature well. Or would it be better to simply use a pot on the stove and stir occasionally? I am not trying to achieve amazing results here, just to get a taste of the technique and see if it really is beneficial for me.
I don't think a thermos bottle will give you enough room to cook much of anything.  However in principle, it could work.  It would be better to use a cooler.  This old Serious Eats article explains everything.  Of course, that was written 8 or 9 years ago, when immersion circulators were very pricey.  You can get them now for as low as $99 US.

You won't need 12 hours (and I wouldn't recommend any long duration cooks without an actual circulator).  You can easily cook a steak (even in a pot in the kitchen sink with running hot water if your water heater puts out high enough heat) in an hour.  You could also do this on the stove top, controlling the burner and monitoring the water temperature, but a cooler will retain the heat and you will be pretty good for a cook of an hour or so.

I've been using sous vide for at least 10 years.  I don't use it for everything.  It's one of a set of kitchen tools.  However, I do find it useful.  Given the current price point, I would say it is worth the purchase.  Plus, then you have the most control, with less monitoring...plus the ability to experiment with much longer cooking times (which impacts texture of proteins).