From my own experiences with both low dose clomid and proviron, i believe that proviron WILL cause some amount of suppression if not straight away then eventually.
My test levels circa 2012, prior to using clomid, averaged in the low 300's. On clomid, low 600's (note - i only had the one blood test after starting clomid (nhs) and didn't test again (private) until i started getting problems).
Around the start of 2017 i experimented with proviron, taking 25mg most working days (not religeously though). At first, i loved the effect it had - more energy, more motivation. The effect seemed to wane after a few weeks, but because i'd read it was non suppressive, took it anyway.
Eventually, due to getting progressively worsening joint problems (knees, hips), i paid and got some private blood work. My test levels came back at 11.7nmol/l (337ng/dl). The clomid was still working fine as my LH was top of the range on just 12.5mg eod. Assuming my LH receptors may have been 'over stimulated' from the constantly raised LH, i dropped the clomid and re tested a month later. My LH had dropped from 8 down to 4 and my test level down to 8.68nmol/l (250ng/dl). Further testing every month or so saw it drop down to 6.04nmol/l (174ng/dl)
During this time i frantically researched into what could have caused my testis to stop responding to LH. The conclusion i came to at first was my age - i was 41 when i got that 600 reading, and 47 when it dropped. At some point though it occured to me that maybe the proviron could have caused it. A bit of trawling through pubmed brought back a study showing proviron IS suppressive. Not against LH, but directly in the testis (i'll try and find the study again).
Now, two years on, i'm not really any better off. I took a bunch of private blood test results to my NHS doctor, but when their test had me come back at 337ng/dl, i got a letter in the post saying he'd spoken to and endo about me and that basically that i'm perfectly fine and that trt is dangerous... I could treat myself (got everything already, enough for the next two years), but every time i decide to start, i read something that'll put me off, and i've been repeating this cycle of nearly doing it for two years.
Sorry, this turned into a rant about my situation!
TLDR - i wouldn't risk playing with proviron unless it was infrequent, and blood work was kept up with.