i recently tried both the tld version and the bob church and i found that the wider tld was alot cumfier all day and that the bob church wasn't wide enough to sit on it all day.
i also thought that the accross the gunnel type seat wasn't that safe(that my opinion and i'm not the most confident of people in a boat)especially if you leaned back a little.
i have been pondering making my own with the wise boat seat which i will be doing in the next few weeks.rotating bracket for £8.00 and some g clamps or small ratchet straps and your laughing and a cost of around £50-£60 if you find a cheap seat to begin with.i have also seen people mounting the tld version to a gunnel board which would be ideal.i did think of using a small step ladder but i will have to investigate further