Just to touch on what others have discussed and hopefully add something into the mix because I considered FUE with a system behind recently...
Going for a full system was an awesome option for me at the time I got my first. It changed my life after I had extreme shedding over 3-6 months. It seemed like I was going to be a NW7 at 30 like my dad.
I rocked the system for 3 years. Every so often a drunk friend of a friend at a party would draw attention to me personally it in a negative way, as though they had been thinking about it prior to getting drunk enough to say something. "Why would you wear that?" etc. and a couple of people I work with asked about it in a less negative way.
The hairline of a system must be glued to perfection if you don't have a style that covers it, so I totally understand where you're coming from. The hairline is so so important and some people just don't suit a fringe.
Sometimes the lace was visible if it popped up at the hairline during a hot day, and for others they certainly noticed that I went from 30% natural density to BOOM a 65% density system with a better hairline. I was out with a lot of acquaintances/sort of friends right after having my first system fitting and two of them were staring and smiling at my hairline. You could tell they wanted to laugh. It really is a shame that we care what these people think when we should only care for what the very few we love and respect think of us. I told those closest to me about the system, but the problem is people change, some friendships fall apart and some of those people have likely told others regardless. At least with areal hairs on the hairline I guess just about no one would notice, so long as the match was perfect.
I grew to not really care what others thought on good days, but our mental health isn't always optimal to be able to think that way.
My hair loss has stabilised a great deal since wearing a system even though I didn't take any meds. It seems that I've followed my mum's family's genetics and not my dads and they have all had thin hair since their mid 20s. I started looking into FUE in my hairline with a hair system behind it quite recently and it seems that it may be a huge hassle to get perfect every time. At least with a system your hair type, colour etc. can be very very close without being perfect as the hair on the top of your head can generally be styled or cut differently to the sides.
I couldn't find any pictures of any posts of people with knowledge that it would work and look natural. With your system you can give or take a few millimetres as to where it sits - especially if the system hair is long-ish. With how messy the glue or tape can get from a partial system with certain scalp types it may end up being detached and cleaned way more than just going for a full system. For me that would likely be every 2 or 3 days. It will make your hair where the system meets it a mess after a few days in my personal experience.
After doing a lot of research on forum posts like this with very invaluable replies and opinions I opted for just getting a full hair transplant. If I were a higher Norwood it could have been a different decision but I'm going for 4500 grafts and thankfully most of that is going on my hairline and mid scalp. I realise it wont be as full as my hair system but I think for me personally using meds and a little but of Toppik where necessary will look for natural and better for my own piece of mind.
I actually used to pull a lot of hair out of my hair system to make it seem more natural and then after 3 months it would look probably less dense than my hair transplant will be!
Just in my experience I think a system with a natural hairline in front would work best if you're quiffing it for example. The more product and less perception of where each starts and ends might work really well, but I do think it could be a time-consuming nightmare regardless of how good it looks. Just make sure either way that it's a very good match! Let us know if you go ahead with it as well. I'd be very interested to know and I wish you the best of luck with it!