We used both Saga holidays and their insurance for a longish period. However, Saga have, in the recent past, changed their underwriter.
In the past it mattered little what pre-existing you had as they would cover you - especially on their holidays - provided you declared all conditions. Additionally there was no additional premium.
Under the 'new' arrangements there are pre-existing conditions that will not be covered; in fact cover will be refused in total even on their holidays. Additionally there are pre-existing conditions for which additional premiums have now become payable.
In general I would say that Saga no longer truly cater for the older person, as they were when family owned, but have become a fully commercial travel organisation. The original concept of a company catering for the elderly to travel regardless of medical conditions - provided the travel was not against medical advice - has been lost.
To my knowledge the remainder of the insurance package is much the same as any other.