There are a few reasons people like the brooch, the first being the most useful in my opinion is that portable skill station effects are twice as likely to trigger. I have used the brooch going from 99-120 cooking and herblore. Getting extra potions and bombs while doing Herblore is really nice and depending when you sell can make Herblore profitable. The cooking using the brooch turned cooking blue blubbers or sailfish into about 1m gp a hour from the extra fish cooked. Secondly, the brooch will spawn a divine blessing. The divine blessing is kind of like the Seren spirits from the grace of the elves. The divine blessing is a yellow ball that needs to be clicked, when clicked it will give random uncommon or rare invention components. It is a skilling version of scavenging 4. Getting rare components does not happen often but when it does it could be worth a couple million gp.
The next effect is from the listed Distractions and Diversions below.
- Repairing Artisans' Workshop pipes: +20% XP.
- Smithing Smithing ceremonial swords: +20% XP.
- Fishing Deep Sea Fishing hub distractions: +20% XP.
- Hunter Capturing chronicle fragments: +20% XP.
- Woodcutting Obtaining bird's nests and divine eggs while woodcutting: +20% chance.
- Firemaking Fire spirits: +20% reward output.
- Mining Mining Rockertunities: +1 multiplier, making the maximum damage multiplier possible x8.
- Archaeology Sprite Focus: +1 multiplier (at 100%), making the maximum sprite multiplier possible x6 at 100% Sprite Focus.
These effects are really nice, using the brooch all the way to 200m Archaeology having the x6 from the sprite is really nice and makes finding artefacts much faster. When combined with randomly finding invention components I think it is a must have for archaeology.
The last effect of this brooch is that it stores up to 1000 decorated urns of each skill. It will keep urns that have not been used yet and will automatically start a new one when the old one fills up. If you have a half filled one in the bank the brooch grabs that one from your bank before starting a new one. I used this while going for 120 fishing and it was really nice just chucking 1000 fishing urns in the brooch and not worrying about it for a while. It also saved me an inventory spot because I did not need one for an urn filling up and the urns not being filled.
I personally wanted the brooch to be buffed when it first came out, even to the point of submitting a question to RSBANDB on how it can be buffed. Jagex never buffed it and just from using it I realized its value. Is the brooch as good as the amulet? Not even close but for anyone going for 120 using a portable it is worth the money to make it or buy it.