This is a difficult one.
It was always my intention to breast feed but we still had a tub of formula powder in the cupboard. This was because there was a risk I may need to be re-hospitalised after the birth and so needed to make sure DS could be fed.
A few days after being at home I was at breaking point one night, I couldn't get DS to attach and he wouldn't stop screaming. I kept trying but I was getting upset and stressed as was DS so At 4am, in desperation, I told my DH to go and make up some formula. By the time he had boiled the kettle, let it cool, made up the bottle and bought it up to me about 25 minutes had passed and in that time calmed myself down and got DS attached. The same thing happened a few nights later but again, by the time DH appeared with the bottle I had managed to start feeding.
I am glad we didn't have any of the pre-made carton because they would have been available to me quickly so I know I would have given them and then would have regretted it afterwards. It's only because the powdered milk took so bloody long that I ultimately didn't give any.
That's not to say it's a bad thing if formula is given but I do worry that if I had given it and saw how easy it was and how effective it was then I would have started to do it regularly as opposed to just 'one offs'. I think that option would have made me give up as opposed to persevering.
However, the knowledge that the formula powder was in the cupboard gave me a sense of comfort. When I look back on those two nights where I asked my DH to make up a bottle, I honestly don't know what I would have done if we didn't have any powder in the house - I imagine I would have felt like my DS was going to starve and put even more pressure on myself and end up in absolute floods of tears....well even more so than I already was. I think the fact that I knew I had the powder and that DH was making up a bottle gave me that security to allow myself to calm down which led to me calming DS down and then I was able to attach him.
So, to sum it all up, my recommendation would be to have some as back up but get the powdered form in the hope it will work for you like it did for me
DS is now 16 weeks and has not had formula since we came home. Yes it's annoying we have an opened tin of formula that has never been used, but the cost of it was well worth it in the long run, just for the security it provided me with.