May Allah bless you.
There is an extensive analysis of the HPP offered by Al Rayan on our website, please see the following link below.
My advice is the following:
If a person is happy to rent or she can afford to buy a property without taking any sort of mortgages, then she should do so. However if she cannot afford to buy it and she needs to take a mortgage, then she should take any Islamic mortgage available in the UK which has been certified by a scholarly panel.
In the case of Al Rayan, their products have been certified by senior reliable scholars.
I do understand that other scholars differ on the Islamic mortgage subject, but we must understand that we are fortunate to have access to Islamic mortgages at all in this country. Yes, some people might feel that the halal mortgage system is not perfect, however improvement can only happen if Muslims support the current system. In fact I have heard Mufti Taqi in a speech saying that Muslims must keep on lobbying with other banks to create alternative Islamic financial products to suit their needs.
As far as the fatwa of IslamQA is concerned, I am not able to comment on it as I do not have sufficient information from the question that was put forward to them.
InshaAllah @Mufti_Faraz_Adam can also share his opinion on this matter.
And Allah knows best!