My DS was in reception last year. It was his 3rd school (due to moving).
1st school - class of 30 yr Rs - full time class teacher and TA - she was studying so had PPA time and at least another half day off a week so DS had a variety of supply teachers for these.
2nd school - class of 30 mixed year Rs and year 1s. Full time teacher and TA
3rd school - class of 11, class teacher 4 mornings a week, head covered all day on 5th day. HLTA who 'provided continuity'.
I had done some voluntary work in the 1st school, so know how the class worked (carpet time, phonics, group time, free play etc).
I had doubts about having a part time teacher, but within 6 weeks of DS being at the 3rd school, Mrs X was established as a very respected teacher in DS's eyes. The proportion of teacher time and attention he had was equal or above what he'd had at the other schools - due to the lower numbers.
Yes the law states this is wrong, but it seems the small schools locally have a choice - 3 classes with FT teachers or 4 classes with a part time teacher in one of the classes. From my experience, this is definitely the best option.
I guess what I'd say to OP in the light of this is go and have a look at the school, meet the HLTA if you can. Has your friend told you about the part time teacher because you 'should be aware...' or because she's a great teacher?
Good luck with your choices!