I like Fenwicks as a degreaser if i’ve let things get ridiculously filthy and need them clean again. That’s when I deploy the FS1 in whatever dilution I see fit – usually 1+9 but I’ve used it much stronger than this on very filthy things before now.
Most of the time it’s over engineered for the job of general bike cleaning and possibly damaging – degreasers and things you don’t want degreasing are a pointless combination. There’s persistent muttering about painted finishes being softened by citrus cleaners and needing a couple of days to reharden although a quick google hasn’t shown up any substantiation for that.
I could see plain soap flake and warm water working well.
I can understand why washing up liquid would be a bad idea as it’s a bad idea for cars too – that salt content. Great for dishes. Car shampoo and I’m struggling to see a downside though. It’s designed for basically the same application and range of finishes, often has desirables like mild wax built in… I’m biassed as I use car shampoo myself when washing bikes, but I can’t see why MucOff or FS1 should be regarded as a better product apart from on the oily bits if they need a degreaser (and they shouldn’t every time, really…) Indeed, if you go and check out MorganBlue bike wash, it’s very much a car shampoo type product and not a MucOff/FS1 type degreaser.