Cash back plans (CASH not gifts) are they worth the effort?

[flannagain]

I have posted this question in Mobile phone & Plans and need another "answer" based in credit finance.

As I understand it agency law covered this area, the cash back problems of the 2007/ 2008 era are now gone
As some of these cashback plans can be very generous are there any protection implicit or explicit?
As with cash it is spread our over the two years whereas a gift is UPFRONT and nothing is in the T&C

Does Agency Law protect me if I take out a contract on network X and the agent goes "bust" the network X becomes responsible, when this can be £180.00 on one contract I saw which can buy a mid range handset

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With the first payment NOT until 6 months and nearly 40 days to make a payment are they really worth the effort?

The advantages is the money back but I can't see if there are any guarantees for this)
The disadvantage are 6 months (for the first payment) and for internet based companies they are somewhat paper based
I have itemised billing which is sent PDF, the companies want PRINTED paper recorded delivery and within a set time frame

Any recommendations as to the best companies ( so far just looked at 2) and what are your experiences.
My "negativity" is due to the earlier cashback debacle, so consider again or avoid

If you have have anything to share it all helps
TA