Reading a story in which characters really do say things such as "By jove" is, I imagine, something of a novelty for most readers but that's part of the fun of reading older fiction and it's nice to read stories that aren't laden with expletives and graphic violence.
Both of these stories are told in the first person (but not the same person) and although each is one half of the same story they are quite different in approach.
The first is told by a square-jawed Boy's Own type and in it Nikola is a shady, rarely seen figure who is painted very much as an archetypal master criminal prepared to go to almost any length to have what he desires.
The second story is, in my opinion, the better of the two. The narrator is a more rounded character than the cardboard cut-out of the first and teams up with Nikola not out of villainy but simply because he's broke and faces prison for being so. However, the greatest difference between these two stories is the potrayal of Nikola himself. Here he's seen more of an anti-hero than a villain, one who does no significant harm to anyone in his quest to find............well, I won't spoil it for you.
Bad points? Well, there is the occasional use of casual racism (usually by the square-jawed narrator of the first episode) but they are very few and far between and not extreme in nature. There are also a few very cheesy romantic moments but again they are brief and infrequent and, if you really can't bear them, they can be skipped without harming the plot.