Any side effects from Infini-B?

Again, that is an old study from 1985 that was limited in what it could determine. Look at the more recent studies that have elucidated the mechanisms. They did those more recent studies because of the older ones to try and fill in the gaps of the older ones. Just take the quote from the study you linked.

Whereas the dose of vitamin B6 in the supplements was previously considered responsible for causing neuropathy [[8], [9], [10]], our previous data indicated that the vitamer present in the supplement is the more important determinant [7]. Of all B6 vitamers, only PN was shown to have cytotoxic effects on cultured neuronal cells. These findings correlate well with in vivo animal studies, where PN induced neuronal damage after intraperitoneal injection, whereas the other vitamers did not induce any damage [11]. Also clinically, the vitamer PN predominantly seems to be causing adverse health effects, as the majority of reported cases to Lareb concerned supplements that contain the inactive vitamer PN. It must be noted that most of the vitamin B6 preparations on the market also contain PN, which could contribute to an overrepresentation of PN induced cases of neuropathy. However, this still highlights that, besides the dose of vitamin B6, the specific vitamer present in the supplements plays an important role in the development of vitamin B6-related neuropathy. Some of the patients reporting neuropathic complaints only used a daily dose of 2 mg vitamin B6, whereas other cases of neuropathy developed after the use of 250 mg. In addition, large differences in plasma levels of PLP between the different cases of B6-induced neuropathies were reported by Lareb [5]. This implies that there seems to be an inter-individual difference in kinetics of vitamin B6 and sensitivity towards its toxicity. Taking into account our in vitro findings, we hypothesized that the accumulation of free PN would be responsible for the toxic effects.

They say right there that pyridoxine is the only one that causes toxicity. Then look at the other conclusions in the study.

As expected, supplementation with PLP did barely increase plasma PN levels, since PLP is pharmacologically active and does not need to be transformed into PN. PN was detectable in plasma (5.9 nmol/L) in only one participant. The detected concentration is comparable with low plasma concentrations of PN in the placebo group reported by Bor et al. [20]. The presence of PN intracellularly or in CSF after PLP supplementation can be explained by the presence of proteins with pyridoxal reductase activity, which was recently revealed in vitro and in vivo by Ramos et al. [19].

So P5P, or PLP as they label it in this study, does NOT increase pyridoxine levels. It was only detectable in one patient at all. The idea that taking P5P, and that it will dephosphorylate to pyridoxine in high amounts, and then that pyridoxine will inhibit phosphorylation back to P5P, is quite literally proven incorrect in the study you linked.

Taking into account our in vitro findings, we hypothesized that the accumulation of free PN would be responsible for the toxic effects.

Free pyridoxine is the issue, and that only happens by taking large amounts of pyridoxine.

Differences in metabolism of PN after supplementation possibly explains the individual differences in sensitivity to the neuropathic effects of vitamin B6. Hence, not only the dose, but also the vitamer present in the vitamin B6 supplements is important for the development of such adverse health effects. This is also presented by the data from Lareb, showing that more than 96 % of the reports is due to the use of PN in the supplements. The fact that the vast majority of the available vitamin B6 supplements contain PN must be taken into consideration here.

Pyridoxine is the issue, not P5P. Moreover, it's only an issue in people with the mutation that prevents them from converting pyridoxine to P5P efficiently. So some people can take high levels of pyridoxine without issue. They study even suggests people taking P5P instead! LOL

Ultimately, instead of lowering the dose, it might be better to replace PN by PLP or PL in the supplements.

So the study literally says what I have been saying. P5P is safe, and does not have the issue that pyridoxine has.