Night and Day.
23 SAS conduct their selection and assessment on the installment plan. They do the course over weekends as opposed to the Regiment's course.
You might use the analogy that most anyone could do Hellweek in 45 minute increments over a year. Its the endlessness that destroys the human will and ultimately vettes the product.
This is not a detrimental statement to the 23 SAS troopers, they are excellent soldiers but not to be confused with the Hereford Regiment. Their budget and "guard" status limits training and capabilities.
Sadly they were sent to Astan with shitty equipment and tasked with some hellacious missions. The results were many injuries and deaths from non-hostile reasons.