Whilst I found the Kindle edition to be clear and reasonably easy to read, I feel that charging 20p per electronic copy when the paper edition is free is a bit steep. Compare this to the Daily Telepgraph where a print subscription is £6.50 per WEEK and the monthly Kindle edition is only £9.99
It is also obvious that not a lot of time or effort has gone into creating a specific Kindle edition - they have just dumped in the newspaper text and a small selection of photos. This can been seen from many references to pictures that aren't there, captions for the (missing) photos added to the end of the articles and articles appearing in the wrong order (for example a comment piece/sidebar appearing before the article it relates to). A quick spell check would not go amiss either!
If the ES produced a good Kindle edition I would have considered paying a small monthly fee but getting a poorly edited edition for £4 per month is not for me.
Sorry ES, but as a long time reader of your paper you have not converted me to your Kindle edition - which is a shame as it is much more environmentaly friendly than all the free paper editions left on tubes, trains, etc.