Like yourself, I first thought that using a DIY snoot using plumbing apparatus would do the work fine, then I dived a couple of years ago with Ajiex Dharma in Bali (he's probably the best guide for Tulamben) who's eagerly using this stuff. He lent me his Retra LSD ...
At the end of the holiday I sent a mail to Retra to purchase my own.
There are lots of supermacro/creative images that I wouldn't be able to create without it : very easy to use, makes it easier to focus, no loss of light, you can add plastic filters in it (you know those thin floppy &square enlarger filters nobody uses anymore since film died)
Maybe the only drawback is that it lacks a "wider angle" limiter that would help lighting up a coral head without spreading the light everywhere, I found sometimes the widest hole without any shape was sometimes too narrow.
For the record, I am NOT selling (and do not consider it in the future) my Retra LSD.
Pls have a look at my Flickr photo gallery
and leave a comment.
Galleries in Pbase :
Ambon & Maluku, Bangka & Bali, Komodo & Maumere, Moalboal, Mabul & Sipadan.
Vanuatu incl.SS Pres.Coolidge wreck.