Searching for Crowhurst-St Pancras illustrates one reason why Trainsplit is better than most other sites.
On southeastern it comes up with a £25 fare. This is a £37.75 Anytime single discounted with Network Railcard. The ticket is Crowhurst to London St Pancras. It doesn't find any advance fares probably because Southeastern doesn't offer Advance fares to St P (while it does to LBG).
On Trainsplit it finds a £14.50 advance fare. This is because it knows to look for tickets to "London Underground Zone 1" as well as "London St Pancras". Southeastern
do offer an advance fare to LU Zone 1 so it finds this.
Trainsplit is generally better than other sites even if it's not offering a split ticket option, because of things like this. I find it's very rare that it fails to find something cheaper or as good as other sites.
It means it'll often give you a wider bunch of options to choose from. The SE site gives you 5 tickets to choose between:
View attachment 447384
Trainsplit gives you 13:
View attachment 447385
That includes a better option if you don't want to be restricted to a certain train with an Advance ticket -
It offers a Super off peak single for £22.30 for example, which the SE site doesn't. It also offers you an off-peak return at £27.35. That's useful to know if you are planning to do the return journey within one month because if so that's almost certainly a better option than the £25 advance. It knows to offer this to you even though you've chosen a single journey rather than a return. Other sites will only show you this if you've specifically asked for a return fare.