We had a similar issue. My son, 5.2, wanted to learn to read in the summer. I wasn't keen to teach him as I really didn't want him to be confused by a different system at school, and I felt quite unequipped to teach him. I really wanted to leave it to the professionals.
He was quite insistent however. The school told me that they teach reading using synthetic phonics and so that's how we approached it. By the time he started school he could decode any 3 letter word very easily and was well on the way to knowing all the two letter digraphs, and decoding much longer words.
Only when he started school did I find out the reading scheme is ORT which is a look and say approach. I was so disappointed as no one told me this! I can see the merit in combining synthetic phonics with look and say (more so down the line). But, initially, it was so frustrating for an enthusiastic and reasonably skilled early reader to be thrown loads of 'tricky' words.
He also quickly worked out he could guess words from the picture, or make good use of the repetition of 'key' words throughout the story. I'm not saying that is a bad thing, but it did make him really lazy about actually tackling 'reading' rather than guessing or repetition.
I read a lot of old threads on here and have bought the Dandelion books, which is 'proper' synthetic phonic reading scheme. You can't guess much from the pictures, and each book practises a specific phoneme/diagraph and builds on previous books.
My son adores them, absolutley adores them. The illustrations really engage him (they are photos with cartoon illustrations on top, sounds hideous but they are quite lovely).
We do his ORT book from school, which takes about a minute (whole other story) and then we read from the Dandelion readers. We've started doing some of the Ladybird 'read it yourself' too, and another Ladybird scheme...Phonic Heros? It's good to mix it up.
I'm less anti 'look and say' than I was. I do think there is a place for it, even for a child that's mostly done decodable synthetic phonic reading. For example, my son reads the word 'couldn't' immediately on sight with no hesitation. He's got that from ORT, nowhere else.
Oooof long post. I think the answer is that the 'right' approach is somewhere in the middle of all the different approaches, and that what is right for one child will be entirely wrong for another.
I hate Biff and Chip. My son thinks they are funny. As long as he's happy reading them I'm ok with that. But I'm absolutely sure it's reading the Dandelion stuff that is pushing on his reading ability (which is excellent), and we're now enjoying rounding things out with the Ladybird books. He is so proud to read a whole story to his younger brother. I think there's a lot to be said for encouraging slightly 'easier' reads for confidence and for reading with expression.
Sorry, I went on a bit! In short, yes I would get some synthetic phonic books.