@CyberGene @David B can you please move this conversation in its own thread? I think it's extremely interesting and deserving that!
If money was no objection, even with the limitations you mentioned, the grand wins hands down. Go for it. Now, you said you certainly won't be able to purchase it after a year, but what are the conditions of the store? Some stores here are flexible, because "customer is king" (or better, can bring the money to a competitor). So, for example, could you rent the GL-10 for a year and then buy the NV-10? Could you rent the GL-10 for 2, 3 or more year and then have all the rental money cover for the purchase, rather than just the last year?
If none of this is an option, are you open to "wasting" all that money just to get the experience? Of course I know nothing about your financial situation (and I don't want to know 🤣) or your pianistic aspiration, but by personal experience with myself and my daughter I can say that there is huge jump in motivation and inspiration at each of these stages (in the order we experienced them):
- old, mid-range digital (ES-X)
- old, but good digital (CA series)
- old, decent upright (Howard/Baldwin 44")
- old, decent grand (Apollo 4')
- new, good digital (Yamaha NU1)
- old, fine grand (M&H 6')
In my experience (and confirmed by my daughter) each jump there is very important, and the latter is fantastic. Now, the GL-10 is not the M&H-AA, but it's not an Apollo either, and for what I remember (I tried it briefly in a store) it's definitely better than the NU1 both in touch and sound.
If we look at the rental price alone, there is no competition: the GL-10 wins hands down against the NV-10. I think the only reason why the price is similar is that after a few years the NV-10 has very little remained value, whereas the GL-10 will still have a lot.
Finally, and most importantly, consider negotiating the purchase price with the shop. Do that before signing the rental agreement, and as part of that! To me the asking price seems a bit too high. See https://www.thomannmusic.com/kawai_gl_30_atx_4_e_p_grand_piano.htm as a comparison. And also see if you have the European version of https://www.pianobuyer.com/brand/kawai/