M&A at big 4 or Tech at IB

Hi Guys, I need some advice on choosing between two jobs. 

Currently a SWE at an IB coming from finance degree background in the UK. Few months back I had applied for an in-house M&A entry level job (not DD) at a big4 and received an offer as I was not sure how I would fare in a tech career.  My current job is okay, I don't hate it but I also don't feel highly motivated and I don't see myself being a SWE long term. My current role pays well considering for a grad position and has a good WLB. My work currently is mostly technical but I prefer a both mix of technical and non technical work. If I stay at my current role, I could potentially move into a BA role (not too keen on this) or a product management role which seems to be a better option.

The work in M&A seems interesting as its a mix of both technical and non technical skills with client exposure along with the opportunity to gain the CFA, however taking into account the WLB and horror stories of big4 I am not too sure if this will wear off after the first 8 months especially as I would be taking around 50% pay cut from my current salary to pursue this job. In short term, this job seems to be a great opportunity to learn the ins and out of industry, build technical and non technical skills, have client exposure and get deal experience providing good exit opportunities to either consulting or corporate development roles. I really like the idea of actually working on projects from start to finish, learning about different industries, how to value a firm and evaluate their growth potential which would be helpful if I ever want to create my own business/start something on my own. The role is also more related to what I studied at uni. I am not 100% sure exactly what role I want to be in, but I want a mix of technical aspects and non technical aspects, not doing the same role day in day out but something challenging and dynamic. Ideally I want to gain a good set of skills and experience to set myself up for senior strategy/leadership position at a firm. 

Having spoken to a few individuals(mostly in tech), most people have advised me stay in tech and seek opportunity at my current bank due to the massive pay cut and big4 being known to underpay you and over work you. I have heard in the UK its easier than the US to move to a MM or BB after a year or two, however not too sure if this is really the case. I want to gain some perspective from those in the industry and any thoughts regarding my situation as I am really torn between the two.