Is typical ebook reader with pdf support enough to read scientific papers

No. Not sufficient. Kindle DX, an almost full-sized page, was not big enough. Refresh rates are not fast enough for flipping back and forth. Zooming interface is terrible. E readers are good for simple flow text, one page after the next. That is not how I read papers. Tablets do much better.

Although my experience in this field is limited, here are a few points I learnt :

The mode of learning should be active. You should scribble, underline, highlight, gnaw or circle or whatever to make sure you understand each and every point the author makes. One can't read papers like a fiction novel. It's not a spectator sport.

Any device which allows you to do the above is good.

On PC you can use xournal. It works really well on Linux flavours. On tablets, you have many options for markup. A somewhat related question regarding the review of papers was asked and gathered some interesting answers: Useful software resources for reviewing papers

Either way the point is to get involved. Personally, my productivity is highest on dead tree version but if that's not possible. I strongly prefer my tablet over the computer since distractions are lower. On my computer, any "instant glorification" distraction is one alt+tab away

I started reading scientific papers on my iPad and now I hardly print any papers at all. I use an application called PDF reader, which also allows one to annotate the pdfs, which is really useful for commenting on student papers. One can make comments using a pen or type them in. Apart from saving trees, it is very handy for collecting and carrying around hundreds of papers (that I'll never have time to read).