I bought the FMBs ones (but on ebay not from their site!) - if you are patient you can get a pair for under £12 incl P&P but you do have to bid on a few sets - I found the ones which ended sunday night went cheapest.
Really like them - freeze the packs then store in a cool bag with two ice blocks, they are still cold enough to bung on after XC whilst I walk him off. They can slip down though - you need to do them tight - but are long enough to still be in contact with the tendons even if they slip.
I tried to find the Puffa ones when I was looking, found only one person who had them on their website so I called them up to order them and they didnt believe me that they sold them! They swore that they didnt sell Puffa cold boots and Id been looking at the wrong website! In the end they realised they hadnt updated their site in a long long time...... So I gave up as simply couldnt find them!
I now use Neo Ice bandages which I find really good. They are cold and draw heat out of the leg, they're not freezing cold like I imagine some boots are but then I dont think they should be too cold anyway. Plus you get the benefits of bandaging after to keep any swelling down etc. They're really easy to re-activate (just put them in a bag of the liquid stuff) and to apply.
I use FMBs too - have 2 sets of inserts and tehy can be microwaved to use at hot packs as well as frozen for cold boots. Stay cold for a good length of time. I got free magnetic inserts with mine. Paid 15 (with flirting
I have a mare with very fine legs so am ultra carefull. I cold hose her post xc and then i use clay ( either ice tight or like ice ) wrap cling film over it and then wrap them up for the night.
Its brilliant as cold boots are only meant to stay cold for the reccomended 20 mins but this clay stays on all night and sooths. It has other properties as well and you just wash it off the next day.
A tub of clay is about £16 but its lasts a fair time. And used together with cold boots/wraps it a great way to sooth tired legs.
I have the puffa ones but I'm not really sure about them as they seem to warm up quite quickly so you have to be vigilant and take them off in time. Aeroborn do very similar ones to the puffa called cool sport. I would like some bonner bandages though.