I no longer work there but did when krushers launched back on the day. Procedures don't often change but this is my take from 18m ago.

The milk mix IS definitely considered a soft serve, but it is 'diluted' per se as it is not supposed to be thick like a soft serve.

For those that have mentioned the cleanliness of the materials - I can't guarantee anyone follows the procedures BUT the mix is thrown out at the end of each day and the machines are almost completely disassembled. All inner parts that come off of the machine are required to be sanitized over night in a proper sanitizing solution and boiled water. The only part that cannot be taken off is washed with soapy water - when the machines are put together in the morning they are sanitized with mixers on etc for 15 mins prior to new mix being made. This means that the part that cannot disassemble is still appropriately sanitized.

I have only worked with a pizza hut soft serve machine but from memory the parts on that particular machine were not able to be disassembled for anywhere near as effective cleaning.
If a store is performing their procedures correctly I would say they are definitely safe and I would choose a krusher over a mcshake.

But again it is one those things you have to make the choice about!!