There are a million different "right" ways to perform a single leg deadlift. When considering exercise form it's not about right vs. wrong, it's about context and justification.
The bent versus straight leg is always a common point of contention with the SLDL. The straight leg requires more mobility and also makes you more likely to externally rotate the working hip. This is part of why I advocate for somewhere in between the two when I’m loading up the deadlift.
As for loading, I love the barbell SLDL. There is no reason why you shouldn’t be able to hit a 1-RM with 50% of your 1-RM deadlift. It won't happen overnight, but then again nothing does in the gym.
Nice infographic presented here of easy variations. 50% of your regular Deadlift 1RM 👀! Shout out to @strengthcoachtherapy for the quality page 👌🏻