Me, myself, and I…

Found online this morning, on a business website: 

[…] designed by myself in conjunction with top British manufacturers.

This features the common error of using 'myself' when the writer means 'me', resulting here in a contradiction: has the writer done the designs alone (which is what 'by myself' means) or with someone else ('in conjunction with')?

The correct way to express this statement would be:

[…] designed by me in conjunction with top British manufacturers.

Similarly, the word 'myself' is not the same as 'I'. It isn't correct to say

John and myself went to the cinema 

when actually

John and I went to the cinema.

You can check which is right by removing the other person from the statement. You  would say

I went to the cinema

not 

myself went to the cinema

so it won't be correct to change the I to myself if someone goes with you!