The main difference is the spool. The Halcyon spool is of a very robust material - that is the primary difference.
The spool featured in the advert/picture on your link is actually the 'coldwater' version of the Defender. If you look at the pricing options, it is £11 more expensive. If you were diving in cold water (UK) and wearing thicker gloves, the Halcyon 'Coldwater Defender' is a good purchase, as it has a wider finger hole for DSMB deployment. The standard Halcyon Defender looks very much like the DiveRite one.
Some of the cheaper spools available (not saying I'd count the DiveRite version as a 'cheap' spool) have a low quality assurance. I've seen some spools where the line is not continuous - and is welded together (a cost saving production measure where odd lengths are used).. this has a significant safety implication - especially where the spool may be used within an overhead environment.
That said, the spools i use typically cost about US$15. Very cheap. They work fine and I view them as 'disposable'. If I have to leave one tied inside a wreck, I am not going to cry over the financial loss involved. The line only lasts me about 6 months anyway, before it degrades to an untrustworthy state...from intensive diving and use within wrecks.
However, with the cheaper spools, I do make sure to reel out the line under some tension and check every inch of it before use (I'd probably do this with any reel I bought).
I've never had a problem with the spool itself breaking, so the 'H' spool seems very 'over-engineered' for the task.
I do always make sure that I get a S/S double ender though.