There are benefits to ensuring your investment accounts (e.g. pension, ISA, Lifetime ISA, or other country-specific equivalents, and an excess in non-tax-advantaged ones) are all in the same place, but it’s not a massive deal if they’re not, especially given the paucity of Lifetime ISA options. As far as the admin goes, it’s more important to make whatever you do habitual and automatic than it is to have all the components of your hifi made by the same brand.