Just been to Malta using Ryan Air from Luton Airport.
I had no trouble with taking my concertina (in a soft bag with a shoulder strap) as my only item of hand luggage. And, likewise, my partner was able to take her mandolin in a soft case with a shoulder strap as her only item of hand luggage (apart from her handbag of course). This was even though if it had been measured it would have been seen to be slightly longer than the maximum length allowed. If we had chosen to take the items as a second items of hand luggage we would each have had to pay £20.50 per flight, ie a total extra cost of £82!
But obviously the mandolin is a few inches shorter than the fiddle.
"I thought I heard the old man say ...!"
Alan