I love EZ Keys - I find it gives me new ideas for chord arrangements, and as a guitar playing non-keyboardist it is a god send. 
 
Is there an equivalent product for realistic strings / orchestration? 

There is a Strings sound pack and Midi pack for EZKeys.

mudgel
There is a Strings sound pack and Midi pack for EZKeys.

Unless I am looking at the wrong thing, that attempts to recreate a Mellotron, rather than real strings (?)

Not quite the depth and versatility of the EZ Keys engine, but NI's Action Strings is great for a non-keyboardist as myself. It has a lot of melodic phrases, variations, and in many time signatures......easy-peasy and lots of fun to play. :))
 
https://www.native-instruments.com/en/products/komplete/cinematic/action-strings/
 
There's a couple of sellers at KVR going for about 1/3 of what NI is selling.  

Marshall

mudgel
There is a Strings sound pack and Midi pack for EZKeys.

Unless I am looking at the wrong thing, that attempts to recreate a Mellotron, rather than real strings (?)

Yes - there is a Mellotron and a Solina string machine so its still very keyboard orientated.
Some of the higher end string packages have tools that may help. Some of Kirk Hunter's libraries for example have phrase generators built in which are a sort of very specifically designed arpeggiator to produce runs etc. and can sound very good if used correctly.
 
Sonokinetic have products like Ostinato
 

 

Mesh
Not quite the depth and versatility of the EZ Keys engine, but NI's Action Strings is great for a non-keyboardist as myself. It has a lot of melodic phrases, variations, and in many time signatures......easy-peasy and lots of fun to play. :))
 
https://www.native-instruments.com/en/products/komplete/cinematic/action-strings/
 
There's a couple of sellers at KVR going for about 1/3 of what NI is selling.  

I've owned Action Strings since I bought K9U a couple of years ago. Never even looked at it until this morning. Thanks for the tip. I'll have to play around with it.

Marshall

mudgel
There is a Strings sound pack and Midi pack for EZKeys.

Unless I am looking at the wrong thing, that attempts to recreate a Mellotron, rather than real strings (?)

I wouldn't let that dissuade me.  Mellotron strings are still sampled strings, so the intent (arranging string lines) is more or less the same.  Same goes for any other instruments that are in the pack.  You can always use this to create a string/flute/whatever performance, then substitute a better library that's more to your liking...
 
FWIW, I don't own this particular EZ Pack - though it's long been on my wishlist! - just sharing my opinion that if you like EZKeys in general, you'll probably find this pack a useful addition to your production toolbox.

Love the EZKeys Mellotron. Didn't like the String Machine presets so passed on that.

You can use EZKeys to lay down a "String" type part and then replace the VSTi later with something that sounds more orchestral strings like.
 
I don't really keep the EZKeys instrument sounds but they're close enough for composition to be replaced before mixing.

Great ideas - thank all. I do like EZ Keys, so the idea of using the Mellotron and then substituting is a good one.