[Thephoenix572]

Are they any good and if so what could I use them for?

[WirralWally]

You'll have to make your own mind up about whether or not they are actually any good.

Here's your starter for 10 (or 35) with a link to a US website:-

http://www.plantea.com/milk-jug.htm

[Yorkie]

I'd have concerns they don't let enough light through.

[Henerz]

Use large fizzy drink bottles , i do and they seem to work well, better than chucking them out 

[grinling]

Prob not, but you could use them as pot holders with a cane through the handle.

[Thephoenix572]

Which plants do you use the pop bottle cloches on and when

[mumofstig]

for when you plant out sweetcorn 

[Thephoenix572]

Ideal I was going to grow sweetcorn this year

[lizt]

hi

 i've used plastic drinks bottles, cut tops off and popped over my newly planted on veg, cabbage, cauli, broccli,strawberry's ect.. just to give them a bit of protection till they get going
also cut top and bottom off and used the 'tubes' for broad beans stop the birds getting to young plants.
 i have seen bottles of all types filled with water or soil and used as weights on fleece and netting.

[shiel]

I find that transparent plastic pop cartons are good. If you get the large ones there even better. Take the lids of an water through the hole. Started all my cabbages in them last year and they were fine.

[SnooziSuzi]

the ultimate things to use could be those water cooler bottles but they're really hard to come by because they're so tough and the bottling companies dont give them up easily!

Maybe google for a company that provides water coolers in your area and see what they do with damaged bottles?