If it were me I'd want to replace that with a proper waste pipe in the knowledge that it's much less likely to be eaten.
You could offer the plumber extra to do the job but to be honest it's not that hard and if you give it a go I doubt you'll fuck it up as much as what is there already.
EDIT Just remember to have the fall going the right way
I was wondering about replacing the flexi pipe rubbish with a "proper" pipe - I assume that's been flung in there as someone couldn't be arsed doing it properly at some point... will have a look at the lenghts & angles and try and work out what i need, cheers
Looking at the picture you posted I cannot see that being put there by a plumber or bathroom fitter even if they did turn up with a labourer by the name of Tonto.
In my experience pros do sometimes use flexi but not for what appears to be a straight run with a 90 degree elbow.
If it were me I'd want to replace that with a proper waste pipe in the knowledge that it's much less likely to be eaten.
You could offer the plumber extra to do the job but to be honest it's not that hard and if you give it a go I doubt you'll fuck it up as much as what is there already.
EDIT Just remember to have the fall going the right way