There's only about 40 tickets worth buying on viagogo (cheapest one at the moment is £51) but until the reasonably priced tickets are gone this is a good deal, and here's why:
You pay MyCityDeal £10 for a £50 voucher. Quidco then give you £5 of that back.
You then goto ViaGoGo and pay them (at time of writing) £51 for a ticket and about £16 in booking fees. Except make that £17 in total 'cos of the £50 voucher.
You then get 7% back from Quidco if you went via them to ViaGoGo, if you only get 7% of the cash you've paid (i.e., minus the voucher's value) that's £1.19 but I wouldn't be surprised if I receive 7% of the total price paid, which is £4.69.
So I've just bought a Stevie Wonder for £10 payable to MyCityDeal, £16 payable to ViaGogo, (£26 total) and I'll be receiving £6.19 or £9.69 cashback, making it somewhere between £19 and ~£15.
Ticketmaster and eBay both cost nearer £60, and certainly not less than £50, so I've saved about 60%.
Why this was rated cold yesterday I have no idea.
Offer apparently expires at midnight but they'll probably just promote it to a different city in the UK instead, you don't have to live in that city to get it.