Lifetime ISA question

[challengez]

Various comparison sites recommend Moneybox as the top Cash Lifetime ISA, but its headline rate drops by 1% at the end of the first year. My son has had his account for 3 years, so has been getting the lower interest rate for 2 years, currently 4% (variable).
He has around £15k in the account (including £3k Government bonus).

He is likely to want to buy within the next 1-5 years, so a Stocks & Shares ISA may be risky. Nevertheless, I'm thinking of suggesting he transfers the account to Dodl, which is a S&S ISA with 5.09% interest on funds left in cash. It has an annual 0.15% fee. So would I be right in thinking he would get an equivalent interest rate of 5.09 - 0.15 = 4.94%? Or am I missing something?

To clarify, the Dodl account is a S&S Lifetime ISA (I didn't make that clear in my post above), so there is no transfer charge.

That sounds right. I'm surprised by the interest on cash rate, so double check the figure but it may well be right at the moment. it will be a variable rate.

For money invested in fund(s) there would also be the fund fee. If he knows he won't buy for 5 years then investing is good, but under 5 years is short time period for an investment, so would stick with cash.