I'm so close to completing my ATPLs I can smell it. I also just about managed it full time. If it wasn't for the fact I worked virtually without holiday last year I would not have been able to blag the six weeks holiday I needed this year to do the ATPLs. That would have been the biggest problem. However, I am doing mine with Bristol who require four weeks class time. However, London Guildhall 'only' require three weeks so depending on your constraints I think plenty of phoning and talking will be required to find the right course for you.
As to whether it was a wise choice, in my case it was the only choice.