Horse transport or self drive??

[SW3]

In the spring I'll be moving my 4yo from my parents place where he grew up in North Wales to his new home near Bristol. My mother is adamant I should use a professional horse transporter (i.e. one of those uber big boxes) rather than drive him down myself on his own (but with me obviously!) in a 3.5tonne box. Am I being stupid even considering driving myself?? ;-) I was wondering what people's experiences have been with horse transporters and what you think the pros and cons are..... I appreciate he may be more chilled with other horses around but is there much chance of argy bargy? and how can I guarantee he has a pretty direct journey? (and doesnt got to e.g. Bristol via Lincolnshire for example - or some other similarly circuitous route!)

Thanks in advance for any views!