Treadle Feeders

I have a big problem with Jackdaws, crows etc coming into the run and eating the hen food.  The area would be very difficult to cover so am thinking of a treadle feeder.  Are there any things I should be looking out for when purchasing one?  I have found one on Regency Poultry which is £29.99 which is very reasonable.  Anyone with experience with these feeders ie, pros and cons etc would be very useful.  Thanks

A treadle feeder is one that can only be opened by the hen standing on the base which opens up the food inside.  Not well explained by me really.  The link is:  http://www.regencypoultry.com/feeders/metalfeeders/treadle_feeder.htm   if you scroll down the page it will show you how it works.  It means that a jackdaw or crow etc shouldn't be able to get at the food because they won't be heavy enough for it to open.  Our run is too big to be able to put netting over it - that would be my first thought but we would have to put posts in the middle to hold any chicken wire or netting up as well as the fact it is not square or rectangular doesn't help either.  I have spoken to Regency Poultry and they are not in stock at the moment but will be getting them in next Wednesday.  I have just changed my hens food and the jackdaws etc seem to think it was bought just for them  
I will let you know if I get one - I think I probably will but would like to hear from someone who has used them.

Hi Joyfull, the one I am looking at is a 10kg feeder but doesn't say whether it is for large fowl or bantams.  I just hope it stops all the wild birds eating all the food!  Do you think the 10kg one will be big enough?  It should be, I only have 5 hens.