If you take the whole pension pot in one go in the UK then the first 25 % is tax free but the other 75 % counts as income in that year and is taxed as such. If you had a salary in that year the 75 % of the pension pot is added to it which could lead to paying very high marginal tax rates on that 75 %, e.g. 40 % on much of it. I wouldn't fancy giving 30 % of my total pension pot to HMRC unless I knew I was going to pop my clogs in a very short space of time. I am not sure what methods companies like Abbey Wealth use to move the pension pot offshore or what tax liabilities those methods incur.
My two pensions were defined benefit schemes that, at the time I started to take, them only allowed up to 25 % to be taken as a lump sum, also tax free. While taking the lump sum reduced the monthly pensions paid I worked out that, even with a small return on capital, it would take me at least 20 years, probably more, to recoup the capital from the lump sum so I took the maximum. Another factor was the dependant's pension. Under the terms of each scheme, if my wife had survived me she would have received 50 % of the pension. Initially I was worried that taking the 25 % lump sum would reduce her pension and make life difficult for her until I discovered that she would receive 50 % of the full pension as if I hadn't taken the cash. Then it was a no brainer.
Not specifically addressing Abbey Wealth but in general I would have two main concerns. Firstly I wouldn't like the idea of trying to seek recompense through the Spanish court system if anything did go wrong. I know little about Spain but I think their court system is approaching as bad as the Greek one. Secondly financial managers are insentivised to arrange your investment in a way that brings them the biggest return in fees rather than you the biggest return on your investment. The really classic example is one chapter of the teamsters union in the USA. That was under the control of the mob who used money in the pension scheme to fund development projects in Las Vegas, casinos and associated hotels, restaurants, bars etc, and then used those facilities to launder the proceeds of their crime activities. Obviously the government didn't like that so they took control of the pension scheme away from the mob and gave it to Goldman Sachs to run. When the mob was running it the scheme was never in arrears, it made very good returns on capital and every retiring teamster received a generous pension. After several years being run by Goldman Sachs it is essentially bankrupt and retiring teamsters in that chapter can look forward to getting a small percentage of the pension they expected. Most of the lost funds have gone to Goldman Sachs in fees as they churned the investments to bring them maximum returns. While Abbey Wealth is clearly not Goldman Sachs or the mob it does illustrate how investment managers can milk your investment. I am not suggesting Abbey Wealth would do that but I am very wary.