Hi, i used it, it is one of the way to keep reciting vocabularies, etc. To me, it is not very useful, but i know it is very powerful. 

I once even made my own decks for others.

By the way, you should not use <em>only</em> flashcards, but it can be one of your main study ingredients, especially in the beginning if you can't follow conversations yet. Don't forget to practise actual use and pronunciation etc.

Yes, I use Pleco a lot (it's only for Chinese). It has a spaced repetition mode, but I mostly use another mode that doesn't depend on time but only on how often you've been correct/incorrect.

I think both modes can work well, spaced repetition is perhaps most useful if you study a fixed amount of time per day or week (which I don't do).

Definitely use some sort of flashcard system rather than reading lists of words; you have to be forced to think about it to remember well. And some sort of system to not repeat words you know too many times is of course much more efficient. Spaced repetition is a good way to do this.

Don't learn words in isolation too much trough. It's fine for things like fruit names, for in general try to learn short sentences so you have at least some context about grammar and ideally also about how the how the word is used (so about meaning).