Hello everyone, I thought I'd post an update/review for future reference.
I bought the Onguard Brute which arrived on monday. I went for the standard length, as I sometimes have to lock up to random objects when out and about and thought that might not be possible with the mini. Also exists in a "long" but I didn't want it to be too huge. The standard suits me fine, and its small enough to easily "fill" the lock, making it harder for anyone to lever it open.
Yes, it's pretty heavy, but not as bad as I was fearing. I nearly always take a rucksack with me anyway so I just shove it in there (it does come with a frame mount, but I haven't put it on yet). Even with shopping etc, I'm not going to win any speed prize but its comfortable enough.
The locking mechanism (so far) is smooth and easy to use, although at first I didn't realise that you have to physically lock it with the key, not just shove the two parts together as you do on my other locks (don't worry, I didn't leave it like that!)
The main thing is the extra peace of mind, it's nice to be able to leave it somewhere and not have to rush/constantly check it's still there