Since I did both further and spec in year 12, I’ll provide you with my insight:
Given the scaling of specialist, it’s quite intuitive that a good score in the subject requires hard work (as with any subject, but particularly in spec). So
if you are a student you has the diligence and dedication, then 100% go for specialist - ultimately the hard work will pay off (at least most of the time... in my case, although I did A LOT of work for specialist during year 12, I really - and I mean, REALLY - slacked off during the exam period, so from getting sac marks of 1 or 2 less than a friend of mine in my class who got a 47 raw, I ended up with a 35. So spec really does require full effort). So in essence, if you maintain a good work ethic and don’t burn out, then you’ll be set for the high 30s/40s raw in spec. In terms of difficulty, it can be quite challenging at times, but it’s certainly doable, so I wouldn’t get bogged down if you can’t complete exam questions yet - you’ll build up the mathematics skills throughout the year. Also, another perk of doing spec is that it really helps with methods: despite being different subjects, there is quite a substantial overlap in the calculus and probability sections, so that’s definitely a bonus for both subjects since you can study a concept which helps both subjects.
In regards to further: as you said, it is extremely easy. I’m not going to lie, the subject can become a joke at times in terms of how easy it is. However, I think a huge misconception is that because further is easy, then getting a 45+ ss is easy as well. Let me just say this:
if you don’t work in this subject, you will not get a 40. I had friends who treated it as a bludge, and they ended up with study scores in the 30s (even though they were extremely capable maths students). Also, if you have a bad day on the exam, say good bye to a high 40 - a friend of mine was full marking nearly every SAC, but dropped 4 marks on the Exam 1, but he aced Exam 2. Unfortunately, he got a 41, just because of that one bad day. One last con: the cohort you are in can certainly make a difference to your score due to the sheer competition. After the exam, I was pretty certain I dropped 1 or 2 marks across both exams (98 or 99/100). Because of this, I thought I’d get a 47-49 score. However, because I was rank 3 and the two students above me sorta bombed the exams (both got low 40s), my SAC marks were pushed down significantly, leading to my underwhelming 45. So taking further is definitely a risk. On the contrary, I disagree with people who claim that further is ‘boring’ - I definitely enjoyed the subject, especially the financial section since it was maths which could be applied to the real world and not just a textbook. Another thing that is really good about further is the Geometry module: in methods (and even spec), you may encounter questions regarding similar triangles, which isn’t really in the methods course, but it is taught in further - this can give you a huge advantage.
So all in all, specialist is the perfect subject if you work really hard; it’s really only worth it for the scaling, so a score >35 is optimal if you are doing spec since you 100% want it in your top 4. In contrast, further is a good 5th or 6th subject since you can get a low 40 with minimal work, but getting a high 40 in it is a bit of a gamble. In my situation, specialist was my 3rd best scaled whereas further was my 5th. Therefore, I personally think specialist is the better option, but it ultimately comes down to your study habits and what you feel more comfortable with...
Hope this helps!