The Desktop version is brilliant in my opinion - and as a ProAdvisor (desktop partner), yes, it's £32 per month (plus VAT!) I have had a number of enquiries from people that are QuickBooks users, but I don't honestly think that the certification has necessarily generated those enquiries - probably more my website, where I stress that I'm a QuickBooks specialist.
If you're unsure about whether to commit to QuickBooks, you could purchase the Pro version of Quickbooks from Amazon for not much more than £100 and this would do the same job and last you for 3 years without any obligation or necessity to upgrade. You would miss out on the support and a free Pro version for resale - but you could always join at a later date if you liked it, got customers with it and wanted to continue with it.
With regards to the Online version - you can sign up free for this, and get your own file for your own business (or practice / sample file) if you get an enquiry from a customer that wanted to use it, or already uses it - you can add them into your package at the cost of £6 per month (at the moment, for the Plus version, which is the top version). This is a 'wholesale' price and allows you to charge the customer a higher amount per month. QuickBooks are currently charging £13.70 plus VAT per month for Essentials, which is the middle version, so I usually find a middle ground for charging, which most clients seem very happy with. So in summary - it wouldn't cost you a bean to get certified with the Online version as training is free, and being a Partner is free....
Having said all this - QuickBooks Online can be a very frustrating package - I'm very close to changing to another package because of it's downfalls - at the moment, it's just its cost that keeps me with it. It has a long way to go before it's any where near as good as it's desktop version - but is Xero and Kashflow any better.............I don't know and wont know, until I try them!!!
Hope this helps