Replacing a Rayburn ignition transformer

Is there anyone knowledgeable in ignition transformers?

I have an oil fired Rayburn and the ignition transformer needs replacing. There is a massive difference in price for the same make of transformer. There is only one difference in the spec of the 2 transformers which I don’t really understand the consequences of using the cheaper one

The one being used says 25% su 4’
The cheap one says. 35% su 4’

All other specs are the same. I.e 240v. 20mA. 14kv

Any guidance would be a help

su simply refers its duty cycle
a greater number is better [more reliable]

simple to change but be very careful theres about +8000 volts flying around

the ones rayburn supply are very expensive for what they are.

done several over the years