Everyone needs to do their own calculations to see what is their best value option.
Aviva charges 0.4% for their Pension plan, which is on the higher end. But prices are around 0.2-0.4%.
For a pot of 50 000, at 0.4% that’s a total of £200 a year. Even if you are not using the ISA, it’s cheaper than keeping the money there. If you have a pension of 40k, paying a 0.3% annual fee, that’s £120, which is the same as Freetrade annual fee.
If you consider that you are paying £5 month for the ISA(and you are using a ISA anyway), the SIPP product cost you £60 a year. That’s exactly a £20 000 pot at 0.3% annual fee. So, if you are using the ISA and have a pension of 20K or above paying 0.3% annually, you are better of on Freetrade. This excluding FX fees, which you can avoid by buying UK based ETFs on your pension. Do you own assessment and cost comparison.