I noticed this check valve or backflow preventer type fitting/valve installed on the hot water line nipple coming out of the old electric water heater I'm replacing because the tank started leaking. Is this very normal that this should be here and should I go ahead and reinstall it in the same place when I install the new water heater?

that is an inline strainer.
someone installed it to try keep the water exiting the tank free of debris.

nice idea but not needed..

[www.reece.com.au]

Then if not needed should I take the trouble/expense eliminating it from the line? That would entail me needing to purchase/install a longer flex line there because the one present now wouldn't be long enough to make the connection without that part there. And, if I do leave it on the line should I maybe try to go ahead and check the strainer inside, just to check it and maybe clean/remove any debris if there is any?

I'd prefer to just re-install it like it is with the replacement water heater and not bother with it unless it would be recommended that I do otherwise.

it is totally up to you.
you can keep it there and either clean it or just remove the insides and leave them out.
it depends on what you find inside of it for debris.

Ok sounds like I should at least try to unscrew that plug I guess and take a look inside, then go from there. Probably will turn the water supply off first. Boy what a fun project. thanks

The way it is installed, anything in the strainer would probably just fall out and down the pipe back into the heater.

i won't coment on the strainer because others have,but i just wanted to say you should replace both supply lines.those tend to get stiff .i use the stainless steel corragated ones.you should use new gaskets at the least. good luck...dan