IMO “SI” products are true DC switching isolators, not an AC type de-rated or re-wired for DC operation. What you have to consider is that any AC isolator is predominantly designed with materials chosen such that the load will be AC, this means that the load supply will be a 50/60Hz sine wave, whether it be 230Vac or 400Vac, etc. When switching AC it should be remembered that the nature of the load supply will always pass through 0Vac and therefore although loads can be arduous in type the supply is self extinguishing – by that I mean that even if the isolator switches at peak load and an arc between contacts is formed the action of the supply reducing to 0V means that the load will tend to zero and the arc be extinguished.
DC load, on the other hand, is always there and unless the load becomes zero the power being pulled through the contacts will always be the same, so if the load is 500Vdc 25A it will be 500V 25A now, in 1s , in 1min, in 1hour – that is constant. If this is the case unlike the AC above if you switch “OFF” on load you will also be switching “ON” on load; DC does not go through a 0V level unless there is system supply failure (or some other fault).