I agree, I don't think it's much cheaper....depending on whether you yourself can cover periods of leave etc. and it is quite complicated to be an employer!
That said, you do have more control as you can employ who you like, and are not reliant on who the agency sends. The PA only has to have whatever level of experience or training is needed for the tasks you want them to do.....so I understand that sometimes it works well to employ someone you know (though you could put a friendship at risk, just as you could in employing a friend to do anything else).
If your loved one is LA funded, you need to ask for a direct payment from their personal budget to pay the PA ( the amount of this depends on the outcome of the community care assessment). You can then use this as you choose, eg to provide 7x twice daily visits, or two long days a week etc.
Lots to think about gilly